Organocatalytic acetylation of pea starch: Effect of alkanoyl and tartaryl groups on starch acetate performance

Organocatalytic acetylation of pea starch was systematically optimized using tartaric acid as catalyst. The effect of the degree of substitution with alkanoyl (DSacyl) and tartaryl groups (DStar) on thermal and moisture resistivity, and film-forming properties was investigated. Pea starch with DSacyl from 0.03 to 2.8 was successfully developed at more efficient reaction rates than acetylated maize starch.

Carbohydrate Polymers 294 (2022) 119780 Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol Organocatalytic acetylation of pea starch: Effect of alkanoyl and tartaryl groups on starch acetate performance Natalia P Vidal a, b, Wenqiang Bai a, Mingwei Geng a, c, Mario M Martinez a, * a Center for Innovative Food (CiFOOD), Department of Food Science, Aarhus University, AgroFood Park 48, Aarhus N 8200, Denmark Aarhus Institute of Advanced Studies (AIAS), Aarhus University, DK-8000 Aarhus, Denmark c School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang 453007, China b A R T I C L E I N F O A B S T R A C T Keywords: Organocatalytic esterification Tartaric acid NMR Packaging Biofilms Chromatography Organocatalytic acetylation of pea starch was systematically optimized using tartaric acid as catalyst The effect of the degree of substitution with alkanoyl (DSacyl) and tartaryl groups (DStar) on thermal and moisture re­ sistivity, and film-forming properties was investigated Pea starch with DSacyl from 0.03 to 2.8 was successfully developed at more efficient reaction rates than acetylated maize starch Nevertheless, longer reaction time resulted in granule surface roughness, loss of birefringence, hydrolytic degradation, and a DStar up to 0.5 Solidstate 13C NMR and SEC-MALS-RI suggested that tartaryl groups formed crosslinked di-starch tartrate Acetylation increased the hydrophobicity, degradation temperature (by ~17 %), and glass transition temperature (by up to ~38 %) of pea starch The use of organocatalytically-acetylated pea starch with DSacyl ≤ 0.39 generated starchbased biofilms with higher tensile and water barrier properties Nevertheless, at higher DS, the incompatibility between highly acetylated and native pea starches resulted in a heterogenous/microporous structure that worsened film properties Introduction Pea starch is, more than ever before, an abundant by-product from the increasing production of protein ingredients from field peas, repre­ senting an inexpensive, non-toxic, and annually renewable starch source compared to wheat, corn, or potato starches (Martinez & Boukid, 2021) Unfortunately, pea starch demand does not match its escalating abun­ dance due to its inherent properties As any other starch, pea starch has several limitations as a replacer of fossil-based polymeric materials, including its lack of intrinsic thermoplastic behavior (Xu et al., 2020), its slow recrystallisation after processing that leads to the progressive embrittlement (Huneault & Li, 2007), and its hydrophilic nature resulting in poor moisture sensitivity Furthermore, the inherent water content of starch can lead to considerable hydrolysis and molar mass decrease during processing (Imre & Vilaplana, 2020) This deserves special consideration in those starches with elevated relative proportion of B-type crystalline polymorphism, such as pea, which possesses 22–55 % of crystals found as B-type allomorph and, hence, with a central cavity with large amounts of water surrounded by six double helices (P´erez & Bertoft, 2010; Ren et al., 2021) Pea starch also has the typical limita­ tions of most starches as a food ingredient or drug excipient, such as poor stability and processing tolerance, high water sorption, low shear, and heat resistance (Cyras et al., 2006; Parandoosh & Hudson, 1993; Shog­ ren, 1996; Singh et al., 2007), and additional limitations due to its amylose-driven shortcomings, including low and slow granular swelling and excessive gel syneresis and stiffness (Martinez & Boukid, 2021) Interestingly, the three hydroxyl groups in C2, C3 and C6 in the anhydroglucose units from starch, which confer the hydrophilic nature to the molecule, are available to be chemically esterified with carboxylic acids, or carboxylic acid anhydrides or chlorides Starches having a low degree of substitution (DS, average number of hydroxyls replaced by other moieties per repeating unit) find numerous applications in the food industry as adhesive, thickening, texturizing, stabilizing, and binding agents (Huang, Schols, Jin, Sulmann, Voragen, 2007a; Imre & Vilaplana, 2020; Ragavan et al., 2022) Moreover, starch esterified with short chain fatty acids (e.g., acetate, propionate, butyrate) have the potential to support the maintenance of a healthy gut (Annison et al., 2003; Clarke et al., 2011; Nielsen et al., 2019) According to the EU Regulation (EC) No 1333/2008 (2008), acetylated starch is listed as food additive (E1420) and can present a maximum level of acetyl groups of 2.5 % as imposed by Commission Regulation (EU) No 231/2012 (2012) and US Food and Drugs Administration (FDA) (2017), which * Corresponding author E-mail address: mm@food.au.dk (M.M Martinez) https://doi.org/10.1016/j.carbpol.2022.119780 Received 23 February 2022; Received in revised form 20 May 2022; Accepted 22 June 2022 Available online 27 June 2022 0144-8617/© 2022 The Authors Published by Elsevier Ltd This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) N.P Vidal et al Carbohydrate Polymers 294 (2022) 119780 corresponds to a DS of 0.097 On the other hand, esterified starches with intermediate (0.2–1.5) and high DS (1.5–3.0) can be used as thermo­ plastic materials with improved thermal stability and reduced moisture sensitivity compared to native ones (Imre & Vilaplana, 2020) Currently, commercial starch esters are produced using carboxylic acid anhydrides and sodium hydroxide (NaOH) as catalyst in aqueous medium at pH 7–9 (Bello-P´erez et al., 2010; Di Filippo et al., 2016; Elomaa et al., 2004; Singh et al., 2004; Xu et al., 2004) However, this starch esterification raises some environmental and safety concerns since a large volume of wastewater and sodium acetate are generated (Aˇckar et al., 2015; Ragavan et al., 2022) In this sense, the use of green organocatalysts with controlled catalytic performance has emerged as a possible efficient solution to replace NaOH A wide variety of organo­ catalysts, such as amino acids and hydroxy acids (e.g., lactic, citric, or tartaric acids), are naturally available from biological sources as single enantiomers with controlled catalytic performance This leads to several remarkable applications in solvent-free and metal-free conditions ideal to modify biopolymers for food packaging, food, pharmaceutical and ´ biomedical applications (Avila Ramírez et al., 2019, 2017, 2014) They can be produced at large scale by biotechnological routes in a straight­ forward and cost-effective manner (Domínguez de María, 2010) and therefore, are cheap to prepare and readily accessible in a range of quantities suitable for industrial-scale reactions Last but not least, natural organocatalysts are insensitive to oxygen and moisture in the atmosphere, so there is no need for special reaction equipment and experimental techniques, and are fully biodegradable, non-toxic and environmentally friendly (MacMillan, 2008) Imre and Vilaplana evidenced that, among many organocatalysts, the hydroxycarboxylic tartaric acid, followed by citric acid, exhibited a relevant catalytic effect in maize starch esterification (Imre & Vilaplana, 2020) Moreover, tartaric acid catalyst was shown to successfully cata­ lyze the esterification of starch with several 1-substituted mono­ carboxylic acid and anhydride derivatives of n-alkanes, including acetic, propionic and butyric acids, at DS maximum of 2.93 (Di Filippo et al., 2016; Tupa et al., 2013, 2015; Nielsen et al., 2018) It must be noted that in these studies the substrate used was maize starch Remarkably, the apparent recalcitrance of native maize starch was greatly influenced by the role of amylose in stabilizing the semi-crystalline structure of maize starch and restricting granular swelling (Imre & Vilaplana, 2020; Luo & Shi, 2012) Although pea starch presents lower granular swelling, less porous granular structure, higher proportion of B-type crystalline polymorphism, and considerably smaller amylopectin compared to normal maize starch (Ren et al., 2021), its recalcitrance towards orga­ nocatalytic derivatization has never been studied For the first time, we systematically report the organocatalytic acylation of pea starch using tartaric acid as catalyst We hypothesize that pea starch exhibits lower recalcitrance towards organocatalytic esterification than maize starch, and that both alkanoyl and tartaryl substitutions, measured by solid-state 13C NMR, affect the performance of the resulting starch acetates Pea starch acetates were studied in terms of chemical structure, molecular weight, granular morphology, crys­ tallinity, and thermal properties Moreover, we investigated the role of the developed tartaric acid-catalyzed pea starches on the mechanical, thermal and water barrier properties of pea starch-based biofilms purity), and lithium bromide were purchased from Sigma Aldrich (Søborg, Denmark) Hydrochloric acid, analytical grade ethanol, sodium hydroxide, phenolphthalein, and glycerol were obtained from VWR in­ ternational (Søborg, Denmark) 2.2 Organocatalytic acetylation The organocatalytic acetylation of pea starch was performed following other studies focusing on maize starch, such as those from Imre & Vilaplana and Tupa et al with some modifications (Imre & Vilaplana, 2020; Tupa et al., 2015) The pea starch: tartaric acid ratio was selected from previous studies (Nielsen et al., 2018; Tupa et al., 2015) L-(+)-tartaric acid (20 g; 0.33 mol) was firstly mixed in 50 mL of acetic anhydride (0.52 mol) in a 100 mL round flask with a magnetic stirrer and a reflux condenser to avoid the loss of acetic anhydride An initial temperature of 70–80 ◦ C was set using a temperature-controlled oil bath When completely dissolved (after 15 min), the temperature was increased to the desired reaction temperature (85, 95, 110, and 135 ◦ C), and 10 g of freeze-dried pea starch was added Reaction times ranging from 30 to h were tested to evaluate the effect of this parameter on the degree of substitution of pea starch After the reaction, the dispersed mixture was cooled down at room temperature and the solid material separated from the solvent by vacuum filtration in a Buchner funnel with Whatman No filter paper To ensure the complete removal of the solvent and organocatalyst, washes with distilled water and with 50 % ethanol were performed Washed acetylated starch was dried overnight in an oven at 40 ◦ C Dried modified starch was milled into powder to remove potential aggregates of starch granules Maize starch was used as a control to compare with pea starch for the kinetics of the esterification reaction Samples were kept under controlled rela­ tive humidity in a desiccator at room temperature until further analysis 2.3 Determination of the degree of esterification by chemical titration Back titration with HCl was used to determine the acyl content and degree of substitution of starch acetates following the procedure from Tupa et al (2015) Briefly, 0.11 g of acetylated starch was dispersed in 20 mL of 75 % ethanol and heated at 50 ◦ C for 30 pH of the sus­ pensions was decreased with 0.1 N NaOH and phenolphthalein was used as indicator Subsequently, 20 mL of 0.1 N NaOH was added prior subjecting the samples to a second heat at 50 ◦ C for 15 Samples were left under continuous stirring at room temperature for 48 h After this time, solutions were back titrated with 0.1 M HCl using the same indicator Native pea starch was used as the control The acyl content and degree of substitution (DS) were determined as follows: Acyl (%) = DS = (Vc − Vs)*0.1*Macyl *10− × 100 W (MGlc *Acyl %) (( ) ) × 100 Macyl − *Acyl % Macyl *100 − (1) (2) Where VC is the volume (mL) of HCl used for the titration of the control, VS the volume (mL) of HCl used in the sample, Macyl is the molecular weight of the acetyl groups (43.05 g/ mol), W is the weight of the dried sample in grams and MGlc is the molecular weight of anhydroglucose (162.14 g/ mol) Reported DS values were the mean of at least repetitions Materials and methods 2.1 Materials and reagents Commercial starch from smooth pea was gently provided by Cosucra Group Warcoing S.A (Warcoing, Belgium) Maize starch was purchased from Ingredion Inc (Bridgewater, NJ, USA) Pea and maize starch were freeze-dried for 24 h prior to use to avoid the interference of moisture in the acetylation process Analytical grade acetic anhydride, L-(+)-tartaric acid (>99 % pu­ rity), dimethyl sulfoxide‑d6 (DMSO‑d6), DMSO (HPLC grade, 99.8 % 2.4 Determination of the chemical structure of starch acetates 2.4.1 Fourier Transform Infrared Spectroscopy (FTIR) Dried starch acetates were analyzed in a Nicolet iS5 Fourier Trans­ form Infrared Spectrophotometer (ThermoScientific, Denmark) attached to an iD5 Attenuated Total Reflectance (ATR) accessory (ThermoScienfitic, Denmark) ATR-FTIR was interfaced to a personal N.P Vidal et al Carbohydrate Polymers 294 (2022) 119780 computer operating under OMNIC software (version 2.11) FTIR spectra of native and esterified starch were acquired between 400 and 4000 cm− at a resolution of cm− using 32 co-added scans The assignment of the bands to the specific functional group vibration mode was made by a comparison to previous studies (Tupa et al., 2013; 2015) 2.6 X-ray powder diffraction patterns The powder X-ray diffraction pattern of the samples were analyzed using a Bruker D8 Discover A25 diffractometer (Bruker AXS, Rheinfel­ den, Germany) equipped with a copper tube operating at 40 kV and 30 mA, producing CuKa radiation of 0.154-nm wavelength The diffracto­ grams were collected in a 2θ angle ranging from to 40◦ with a step size of 0.02◦ 2.4.2 Nuclear magnetic resonance 2.4.2.1 Proton Nuclear Magnetic Resonance (1H NMR) Native and acetylated starch (10 mg) were dissolved in deuterated dimethyl sulf­ oxide (DMSO‑d6, mL) (Sigma-Aldrich A/S, Copenhagen, Denmark), and incubated at 100 ◦ C until a complete solubilization was achieved Immediately before analysis, 600 μL of clear solutions were transferred to mm NMR tubes Samples were analyzed on a Bruker Avance III NMR operating at 600.13 MHz The experimental conditions were spectral width, 5000 Hz; relaxation delay, s; number of scans, 64; pulse width, 90◦ , with a total acquisition time of and 49 s The experiments were carried out at 25 ◦ C Due to the hygroscopic nature of the DMSO‑d6, and to avoid starch retrogradation, samples were freshly prepared before each analysis Residual non-deuterated DMSO signal at 2.549 ppm was used as a reference The spectra obtained were analyzed using MestReNova software (version 14.2.1) (Mestrelab Research S.L., Santiago de Compostela, Spain) The acetylation degree of pea starch acetates was calculated by using the ratio of the signal area of the pro­ tons corresponding to the -CH3 acyl group (Aacyl) centered at 2.07 ppm and the area of the signals between 3.2 and 5.5 ppm representing the protons of anhydroglucose units (AGlc), by using the following equation: / Aacyl 3*Aacyl DS = (3) = 7*AGlc AGlc /3 2.7 Molecular size distribution and weight average molecular weight (Mw) Molecular weight distribution of fully branched native and acety­ lated starch was determined following the procedures described by (Martinez et al., 2018) and (Roman et al., 2019) Briefly, 8.0 ± 0.5 mg of starch was dissolved in 1.5 mL DMSO (Sigma, 99.8 % purity) at 80 ◦ C in a thermomixer (Eppendorf, Hamburg, Germany) at 350 rpm for 24 h Samples were then centrifuged at 4800 rpm for 15 and the super­ natant was collected Starch was precipitated with 10 mL 95 % ethanol, the pellet was collected after centrifugation (4800 rpm, 15 min, ◦ C) and resuspended in 1.5 mL of DMSO containing 0.5 % lithium bromide (w/w) The mixture was dissolved at 80 ◦ C and 350 rpm overnight After centrifugation (7000 rpm, 10 min), the supernatant was transferred to a vial for further analysis by High Performance Size Exclusion Chroma­ tography (HPSEC, Agilent 1260 Infinity II, Agilent Technologies, Waldbronn, Germany) connected to a Multi-Angle Laser-Light Scat­ tering detector (MALS) (Wyatt Technology, Santa Barbara, CA) and a refractive-index (RI) detector (Shodex RI-501, Munich, Germany) An injection volume of 100 μL of starch solution was eluted using DMSO/ LiBr as solvent at a 0.3 mL/min flow rate and 80 ◦ C Size separation was performed in GRAM 3000 and GRAM 30 (PSS GmbH, Mainz, Germany) columns connected in series Data to calculate weight average molecular weight (Mw) were analyzed by ASTRA software (version 8.1; Wyatt Technology, Santa Barbara, CA) using a second-order Berry plot pro­ cedure The specific refractive index increment (dn/dc) was set as 0.066 mL/g as previously reported in other starch dissolved in DMSO (Roman et al., 2019) and second viral coefficient (A2) was assumed to be negligible Aacyl and AGlc were normalized according to the number of protons (3 and 7, respectively) contributing to the area of the spectral signals 2.4.2.2 Solid state SP and CP/MAS 13C magnetic resonance Native and acetylated pea starch were analyzed by solid-state 13C NMR following the procedure from (Nielsen et al., 2018) All solid-state NMR spectro­ scopic experiments were performed in a Bruker Avance 400 NMR spectrometer operating at 400.13 MHz and 100.63 MHz for 1H and 13C respectively Solid State Single Pulse (SP) and Cross-Polarization Magic Angle Spinning (CP/MAS) NMR experiments were recorded at 300 K A CP/MAS probe for mm rotos using a spin-rate of kHz, a radio fre­ quency of 70 kHz, spectral width of 50.13 kHz was selected 1H decoupling was applied Recycle delays of 16 and 128 s were used for CP and SP/MAS, respectively Determination of the degree of substitution of starch acetates (DSacyl) and the formation of starch tartrates (DStar) was done by calculating the ratio of the areas of the signal due to the carbon of the acyl group bonded to the carbonyl group (16.56 ppm) or to the carbonyl carbon in the acid/ester (166.88 ppm), respectively, to that of the glucose anomeric carbon of the anhydroglucose units in the starch (91.02 ppm) The ratios were determined from the spectra of 13C SP/ MAS NMR due to the different longitudinal relaxation times of the hydrogen bearing carbons and the carbonyl groups (Nielsen et al., 2018) 2.8 Thermal properties Thermal properties of native and acetylated starch samples in dry state (moisture content 0.05) However, after h, the catalyst competed with the acetic anhydride, resulting in up to 16 % of the total esterification ruled by tartaric acid in h (Table 1) NMR data clearly confirmed that the DS by the chemical titration method is N.P Vidal et al Carbohydrate Polymers 294 (2022) 119780 accurate and reliable when measuring at low DS values in organo­ catalytic reactions; nevertheless, the interaction of tartaric acid with the hydroxyl groups of the anhydroglucose residues at longer reaction times led to an overestimation of the DS values This phenomenon agreed with previous studies in which the contribution of tartaric acid in substitution reactions with maize starch was demonstrated by HPLC-UV (Imre & Vilaplana, 2020) Likewise, Nielsen et al determined the degree of butyrylation of maize and potato starches by 13C-SP- and CP/MAS-NMR and reported overestimations between 38 and 91 % of the DS value by the chemical titration (Nielsen et al., 2018) In our study, the derivati­ zation of pea starch was mainly ruled by acetylation (from 100 % at ≤1 h reaction times to 84 % at reactions times up to h) and not by tartrate formation The low reactivity of tartaric acid, and the efficient acetyla­ tion process of pea starch, were likely the result of several factors, such as the type of acyl donor used (anhydride instead of acid), the low water content of the starch sample due to the drying step prior to the reaction, as well as the short carbon chain-length of the acyl donor reagent (Imre & Vilaplana, 2020) It is worth noting that, due to the dihydroxy dicarboxylic nature of tartaric acid, a possible formation of diacetyl tartaric acid anhydride and further esterification of the acyl groups with the starch cannot be ruled out (Tupa et al., 2020) Likewise, the dihy­ droxy dicarboxylic nature of tartaric acid could likely result in cross­ linked di-starch tartrate, which notably decreased its solubility in organic solvents (Fig S1) acetylation of maize starch with classical NaOH (Xu et al., 2004) or tartaric acid-catalyzed reactions at intermediate DS (Imre & Vilaplana, 2020), which has been suggested to be advantageous in the composites of starch with synthetic polymers as this could improve interfacial adhesion (Imre & Vilaplana, 2020) Even in the absence of water, NPS showed a gradual loss of bire­ fringence at increasing reaction times, indicating a continuous breakdown of the crystalline structure during acylation X-ray diffraction patterns revealed the characteristic C-type polymorphism with peaks at diffraction angles 2θ of 15.1◦ , 17.1◦ , 18◦ , and 23◦ (Fig 3b) On one hand, organocatalytic acetylation did not alter the number and position of the diffraction peaks On the other hand, it resulted in a progressive loss of the intensity of all peaks, which followed a similar trend to that of birefringence and evidenced a continuous breakdown of the crystalline structure during acetylation This occurrence has also been reported for tartaric acid catalyzed maize starch using acetic anhydride as acyl donor, which was attributed to the introduction of acyl groups during the esterification reaction (Tupa et al., 2020) and to the potential plas­ ticizing effect of the side-product of the reaction, acetic acid (Imre & Vilaplana, 2020) Interestingly, even high-DS anhydride-treated samples (DSacyl ~ 3) retained their distinct granular structure (see APS-3 h in Fig 3a) This event could be the consequence of the formation of crosslinked di-starch tartrate, as 13C-SP/MAS NMR data suggested (Table 1), which would result in a cross-linked external shell that pre­ vents granular disruption, as suggested by Tupa et al., 2020 The SEC-RI elution profile of NPS displayed two distinct peaks for amylose and amylopectin molecules separated at ~14 mL elution vol­ ume, both represented by a single peak in the MALS detector that cor­ responded to a weight average molar mass for amylopectin molecules of 7.49 × 106 g/mol (Fig 4a, Fig S3) These results agreed with previous studies using pea starch (Martinez et al., 2018) It is noteworthy that with the sample concentration and injection volume used in this study and amylose molecules being highly polydisperse, they not exhibit detectable laser-light scattering signals, as shown before (Roman et al., 2019) Generally, tartaric acid catalyzed esterification caused a gradual shift of the peaks towards higher elution volumes, confirming hydrolytic degradation and a consequent molar mass decrease (Fig 4a, Table 1) Similar findings were already reported before for maize starch esterified with acetic anhydride, which was explained by the effect of high tem­ peratures in acidic environment (Imre & Vilaplana, 2020) The reaction also decreased the area under the peaks and resulted in a monomodal size distribution, which could result from the coelution of amylose and amylopectin fragments and the fact that low molar mass fractions might be particularly hydrolyzed and washed out of the sample during the 3.3 Effect of tartaric acid catalyzed acetylation process on starch granular morphology, birefringence, crystallinity, and molecular weight (Mw) Native pea starch granules exhibited oval, spherical, kidney and irregular shape and a bimodal size distribution, although the large population of granules (~40 μm of mean diameter) was significantly more dominant (Fig 3a) The observation of NPS granules under polarized light exhibited the typical birefringence attributed to their radial crystalline structure (Fig 3a) Morphology and birefringence were not altered during acetylation at reaction times ≤1 h (APS-0.5 h and APS-1 h), i.e., starch acetates with DSacyl ≤ Similar findings were reported for organocatalytic esterification of maize starch at low DS (Tupa et al., 2013) Nevertheless, acetylation at longer reaction times resulted in a gradual increase of granular surface roughness, decrease of birefringence, and the appearance of granular aggregation At 3–4 h reaction time (DSacyl ~ 3), fusion of granules, alongside a dramatic in­ crease in surface roughness and a complete loss birefringence were detected Increase of roughness upon acylation was also observed in the Fig a) Visual appearance and morphology of native (NPS) and acetylated pea starch (APS) granules under the light (upper) and polarized light (lower) mi­ croscopy Acetylation reaction temperature was 135 ◦ C and the granules were obtained after different reaction times that resulted in different DS From left to right: NPS, APS-0.5 h (DSacyl = 0.39), APS-1 h (DSacyl = 1.00), APS-2 h (DSacyl = 2.23), APS-3 h (DSacyl = 2.80), APS-4 h (DSacyl = 2.63) b) X-Ray diffraction patterns of NPS and APS at different reaction times N.P Vidal et al Carbohydrate Polymers 294 (2022) 119780 Fig a) SEC elution profiles of native (NPS) and acetylated (APS) pea starch at increasing reaction times (0.5 h to h) and constant reaction temperature of 135 ◦ C obtained by HPSEC-MALS-RI b) Thermal stability represented as weight loss (%) as a function of temperature (upper chart), as well as the derivative mass loss (lower chart), determined by TGA c) Thermograms showing the glass transition temperature (Tg) measured by DSC APS-0.5 h (DSacyl = 0.39), APS-1 h (DSacyl = 1.00), APS2 h (DSacyl = 2.23), APS-3 h (DSacyl = 2.80), APS-4 h (DSacyl = 2.63) purification Interestingly, the rate of molar mass decrease with time was significantly lower at longer reaction times, and even the weight average molar mass increased from to h of reaction (Table 1) This occurrence supports 13C-SP/MAS NMR data and the idea that tartaryl esterification formed crosslinked di-starch tartrate due to the dihydroxy dicarboxylic nature of tartaric acid was attributed to the release of acetic acid from anhydroglucose units (Imre & Vilaplana, 2020; Thiebaud et al., 1997; Tupa et al., 2013) Results showed that tartaric acid catalyzed acetylated pea starch of DSacyl ≥ 2.6, whose lower temperature degradation step was completely eliminated, presented an enhanced thermal stability despite their molar mass decrease and loss of crystalline structure The substitution of the hydroxyl by alkanoyl groups in the modified starch seem to avoid interand intramolecular dehydration reactions ruling the decomposition of pea starch We also investigated the effect of acetylation on the glass transition temperature (Tg), which was revealed after a second heating run during DSC analysis (Fig 4c) Native pea starch (NPS) displayed a Tg of 110.8 ◦ C (Table 2) It is well known that the crystalline structure of starch granules acts as physical cross-linking avoiding the mobility of the polymer chains (Mizuno et al., 1998) In this regard, a decrease in Tg upon acetylation was expected as a consequence of the gradual decrease of crystallinity (Fig 3b) and molar mass (Fig 4a) However, Tg gradually increased from 110.8 ◦ C (NPS) to 153.6 ◦ C (4 h reaction), which could be explained by the increase in DS of tartaryl side groups (Table 1) Spe­ cifically, tartaryl esterification would reduce the molecular mobility, either through strong hydrogen bonding of tartaric acid with other starch chains hydroxyl groups (Imre & Vilaplana, 2020), or more likely by the formation of covalent crosslinked di-starch tartrate, as suggested by the SEC-MALS-RI molar mass distributions (Fig 4a) Overall, results demonstrated that tartaric acid catalyzed acetylation of pea starch with acetic anhydride significantly increased its degrada­ tion temperature and Tg, a key factor to broadening its processing temperatures 3.4 Hydrophilicity and thermal stability of tartaric acid catalyzed pea starch acetates Starch hydrophilicity, one of its main shortcomings for many appli­ cations as biomaterial, was indirectly investigated from the first weight loss shown in the TGA weight-loss and derivative mass loss curves (Fig 4b) Native pea starch depicted a first weight loss of ~10 % (be­ tween 45 and 140 ◦ C and a maximum peak at 85.5 ◦ C) due to the evaporation of the remaining water bound to starch (Di Filippo et al., 2016; Tupa et al., 2013) Interestingly, this loss was indirectly correlated with DSacyl (p < 0.001; R2 = 0.983), demonstrating that starch hydro­ philicity was significantly reduced by acetylation The decomposition temperature of starch samples, and hence their thermal stability and processability, increased with the degree of acet­ ylation Native pea starch showed a single weight loss peak at a maximum of 318.9 ◦ C As acetylation time increased, a second weight loss step at higher temperature appeared (369.3–374.5 ◦ C) with the concomitant dissipation of the lower degradation step This phenome­ non was also observed to occur during the tartaric acid catalyzed esterification of maize starch (Elomaa et al., 2004; Imre & Vilaplana, 2020; Tupa et al., 2013) The first step corresponds to the condensation of the remaining non-esterified -OH groups, whereas the second peak N.P Vidal et al Carbohydrate Polymers 294 (2022) 119780 starches (Colussi et al., 2017; El Halal et al., 2017) Table Glass transition temperature (Tg) and thermal degradation (Td) of native (NPS) and acetylated pea starch (APS) studied by DSC and TGA, respectively Tg (◦ C)* Td1 (◦ C) Area Td1 (mg/oC) Td2 (◦ C) Area Td2 (mg/oC) NPS APS-0.5 h APS-1 h APS-2 h APS-3 h APS-4 h 110.8 ± 2.2c 318.9 ± 0.6a 19.5 ± 0.1a – 136.6 ± 3.4b 313.7 ± 0.9b 6.7 ± 0.2b 373.8 ± 0.4ab 2.2 ± 0.1c 129.5 ± 2.6b 289.2 ± 2.4c 1.7 ± 0.1c 374.1 ± 1.3a 9.4 ± 0.2b 130.3 ± 2.9b – 137.1 ± 2.8b – 153.6 ± 5.6a – – – – 369.3 ± 0.4c 21.3 ± 0.2a 374.5 ± 0.7a 22.9 ± 0.3a 372.3 ± 0.1ab 19.3 ± 3.9a – 3.6 Thermal and mechanical properties and Water Vapor Permeability The thermal decomposition of the biofilms studied by TGA revealed four degradation steps attributed to the main components of the biofilms (Fig 6a) Biofilms showed a first peak corresponding to the remaining bound water between 50 and 150 ◦ C, with a maximum peak near 80 ◦ C The weight loss % was ~6 % in NPS biofilms and a gradual loss decrease occurred when using intermediate [BAPS-0.5 h (~4.7 %)] and highly substituted APS [BAPS-1 h to -4 h (~4.1 to 4.5 %)] This event evidenced the enhanced moisture resistivity of APS biofilms compared to its NPS counterpart The first decomposition step of APS films was detected in the range of 208 to 218 ◦ C (Td1), which was absent in NPS films (Table 3) Since the decomposition of the glycerol plasticizer occurs between 150 and 290 ◦ C (Sanyang et al., 2015), we believe this degra­ dation step corresponds to the degradation of glycerol that is poorly interacting with starch in APS-based films Specifically, the mass loss at this temperature increased with the degree of substitution A second degradation step occurred in the range between 320 and 324 ◦ C (Td2), which was attributed to the decomposition of native starch Logically, the area of this step decreased as DS increased, since technically there is less non-esterified starch present in the films No major differences were detected in Td2 with the degree of acetylation A third degradation peak in the range between 364 and 368 ◦ C appeared in APS films (Td3), which by all likelihood represents the decomposition of alkanoyl groups in the modified starch (see Section 3.4) As previously reported, acetylation limits intramolecular dehydration of polysaccharides by reducing the hydroxyl groups (Aburto et al., 1999; Fundador et al., 2012), which, in turn, delays the initiation of thermal decomposition The mechanical properties of APS-films were measured under ten­ sion, and the tensile strength (MPa), elongation at break (%), and Young's Modulus (MPa) were determined from the stress-strain curves of each film (Fig 6b, Table 3) NPS films exhibited mechanical properties similar to those reported in other studies for pea starch films (Cano et al., 2014) The tensile strength and Young's Modulus significantly increased when using APS at low degree of substitution (DSacyl = 0.39), compared to native starch films The reduction of intermolecular interactions within the starch phase as a consequence of surface lamellar acetylation in low DS starch could explain the alteration of the blend morphology and decreased particle size (as observed in Fig S4) We believe that this occurrence could lead to a more homogeneous dispersion of the dispersed phase It is noteworthy that at short reaction time, APS showed molar mass above 2.65 × 105 Da, which is significantly higher than that reported for tartaric acid catalyzed maize starch using acetic acid (Imre & Vilaplana, 2020) Therefore, the reduction in molar mass could have played a minor negative role in APS-0.5 films Nevertheless, APS with higher DS showed a gradual decrease in the tensile strength and Young's Modulus as DS increased (Table 3) The same mechanisms * Tg, glass transition temperature measured in a second heating cycle by DSC Td1 and Td2 represent the degradation peaks detected by TGA Values are expressed as average (n = 2) ± standard deviations Values followed by different letters within each parameter (row) indicate significant differences (p ≤ 0.05) -, not detected 3.5 Film-forming properties of tartaric acid catalyzed APS Since tartaric acid catalyzed acetylation of pea starch significantly enhanced its moisture resistance and thermal stability, we investigated the role of an increasing degree of substitution on the film-forming properties of APS Firstly, freestanding biofilms with APS as the only matrix polymer were made by solvent casting Nonetheless, cohesive films were not attained even using the acetylated pea starch with the lowest DS (DSacyl = 0.39) Hence, NPS/APS blends (3:1 w/w) were prepared instead, which allowed us to understand the effect of DS on film properties, and the compatibility of APS with its native counterpart, NPS NPS films were clear, transparent, and presented a smooth surface (Fig 5a) When adding acetylated starch at DSacyl ≤ 0.4, films were still transparent and smooth, although certain evidence for phase separation was already visible Biofilms became gradually and visibly rougher, darker in color, less transparent and thicker as APS with higher DS was used (Fig 5b-f, Table 3) This could be explained by two factors Firstly, the substitution of -OH groups with hydrophobic monofunctional re­ agents would not only decrease inter- and intra-molecular interactions within the polysaccharide phase, but it could also lead to less adhesion at the interface between the composite components This could result in meaningful phase separation and deterioration in APS film properties (Imre et al., 2019) In fact, sharp edges and large cavities were observed around the starch granules in the films made with APS at high DS (Fig S4) Secondly, the decrease of molar mass during acetylation could have lowered the availability of chains for matrix interaction Likewise, a darker color was expected due to the dark color that results from acetylation (Fig 3a) It is noteworthy that the low standard deviation in film thickness evidenced the uniformity of the films These values agree with the thickness of other biofilms made with acetylated barley and rice Fig Biofilms made of (a) native pea starch, and blends of native: acetylated (3:1, w:w) pea starch of (b) APS-0.5 h (DSacyl = 0.39), (c) APS-1 h (DSacyl = 1.00), (d) APS-2 h (DSacyl = 2.23), (e) APS-3 h (DSacyl = 2.80), (f) APS-4 h (DSacyl = 2.63) N.P Vidal et al Carbohydrate Polymers 294 (2022) 119780 Table Mechanical, thermal and barrier properties of biofilms made with native pea starch (BNPS) or native/acetylated pea starch blends (BAPS) at a 3:1 ratio (w/w) BNPS BAPS-0.5 h BAPS-1 h BAPS-2 h BAPS-3 h BAPS-4 h Mechanical properties Thickness (mm) Tensile Strength (MPa) Elongation at break (%) Elastic modulus (MPa) 0.09 ± 0.00c 17.8 ± 1.3b 4.3 ± 0.1ab 804.9 ± 14.4b 0.08 ± 0.00c 20.1 ± 1.7a 2.4 ± 0.7b 1003.5 ± 136.2a 0.10 ± 0.00b 13.9 ± 0.8c 3.1 ± 0.3b 689.3 ± 83.0c 0.11 ± 0.00a 7.1 ± 0.4d 5.4 ± 0.7a 332.5 ± 43.6d 0.11 ± 0.02ab 6.4 ± 0.9d 5.6 ± 0.5a 263.6 ± 25.7d 0.12 ± 0.01a 5.8 ± 0.3d 3.8 ± 0.5b 302.7 ± 10.8d Thermal stability (TGA) Td1 (◦ C) Area Td1 (mg/ oC) Td2 (◦ C) Area Td2 (mg/ oC) Td3 (◦ C) Area Td3 (mg/ oC) – – 320.6 ± 2.9b 17.6 ± 2.2a – – 208.8 ± 2.6b 1.3 ± 0.1d 323.1 ± 0.1ab 11.6 ± 0.3b 368.3 ± 0.8a 0.7 ± 0.1c 218.8 ± 0.5a 1.5 ± 0.0cd 323.5 ± 0.5ab 11.0 ± 0.2b 367.1 ± 0.6ab 1.7 ± 0.0a 207.1 ± 6.7b 1.6 ± 0.0bc 324.1 ± 0.4a 10.1 ± 0.7b 367.1 ± 0.4ab 1.7 ± 0.1a 214.5 ± 0.0ab 1.8 ± 0.1ab 324.2 ± 0.5a 9.6 ± 0.0b 365.7 ± 0.7b 1.4 ± 0.1b 214.3 ± 1.9ab 2.0 ± 0.0a 322.2 ± 0.7ab 10.7 ± 0.4b 364.0 ± 0.5c 0.4 ± 0.1d Water Vapor Permeability (WVP) WVP (g⋅mm)/(m2⋅day⋅KPa) 1.03 ± 0.07ab 0.74 ± 0.09c 0.92 ± 0.00b 1.11 ± 0.02a 0.93 ± 0.01b 1.02 ± 0.08ab Values followed by different letters within each parameter (row) indicate significant differences (p ≤ 0.05) Td1, Td2, and Td3 represent the degradation temperature peaks detected by TGA -, not detected BAPS-0.5 h (DSacyl = 0.39), BAPS-1 h (DSacyl = 1.00), BAPS-2 h (DSacyl = 2.23), BAPS-3 h (DSacyl = 2.80), BAPS-4 h (DSacyl = 2.63) Fig a) Thermal stability of native (BNPS) and acetylated pea starch (BAPS) biofilms, made with acetylated pea starch at different DS, represented as weight loss (%) as a function of temperature (left), as well as the derivative mass loss (right), determined by TGA b) Strain stress curve of BNPS and BAPS biofilms APS-0.5 h (DSacyl = 0.39), APS-1 h (DSacyl = 1.00), APS-2 h (DSacyl = 2.23), APS-3 h (DSacyl = 2.80), APS-4 h (DSacyl = 2.63) governing film roughness and transparency (see Section 3.5) could also explain mechanical properties Schmidt et al also reported improved tensile strength at low DS values and poorer mechanical resistance at high DS investigating NaOH catalyzed acetylated cassava starch biofilms (Schmidt et al., 2019) The elongation at break (EB%) using APS DSacyl ≤ was similar or slightly worse than that of NPS films (Fig 6b, Table 3), in agreement with other low acetylated starch films (L´ opez et al., 2011; Schmidt et al., 2019) Nonetheless, EB% improved when APS DSacyl > was used in comparison with the control NPS film The retained crystallinity of low acetylated starch probably makes these 10 N.P Vidal et al Carbohydrate Polymers 294 (2022) 119780 films more brittle and less flexible than highly acetylated starch films in which the crystallinity was lost Interestingly, a gradual decrease in the EB% was observed from h to h, which was likely the result of the reduction of molecular mobility and increase in rigidity due to tartaryl esterification and/or crosslinked di-starch tartrates formation The Water Vapor Permeability (WVP) of the native and APS films was measured to assess their potential as barrier materials (Table 3) NPS films possessed a WVP of 1.03 ± 0.07 g⋅mm /m2⋅day⋅KPa, which is in accordance with other values reported for starch-based films (El Halal et al., 2017) The incorporation of APS-0.5 significantly reduced the WVP of the films due to the reduced hydrophilicity of starch acetates (see Section 3.4) Nonetheless, highly acetylated pea starch films (DSacyl ≥ 1) did not show significant differences (p > 0.05) with the control, which, by all likelihood, is the consequence of phase separation resulting in a heterogenous and microporous structure from which water vapor can permeate (Fig S4) Methodology Mingwei Geng: Investigation, Methodology Mario M Martinez: Conceptualization, Methodology, Supervision, Project administration, Funding acquisition, Formal analysis, Visualization, Writing – review & editing Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper Acknowledgments This research was funded by Aarhus University Research Foundation (Aarhus Universitets Forskningsfond, AUFF), project number AUFF-F2020-7-5 The authors would like to thank Laura Roman for her assis­ tance in the analysis of starch molecular weight, as well as Thomas Vosegaard and Dennis Wilkens Juhl for their assistance in the solid-state NMR analysis The authors also thank Cosucra which generously sup­ plied the raw pea starch Conclusions In this study, we systematically reported the organocatalytic acyla­ tion of smooth pea starch using tartaric acid as green catalyst and acetic anhydride as acyl donor Pea starch was less recalcitrant towards organocatalytic esterification than maize starch, as indicated by the faster reaction kinetics and higher degree of substitution observed in the former The degree of substitution with alkanoyl (DSacyl) groups was validated using FTIR, 1H NMR and solid-state 13C NMR However, only NMR displayed good specificity and 13C-SP-NMR enabled the quantifi­ cation of the degree of substitution by tartaryl groups (DStar) Pea starch with DSacyl from 0.03 to 2.8 was successfully developed, with granular and crystalline structure mostly retained until DSacyl ≤ 1.0 Longer re­ action time resulted in starch granule surface roughness, loss of bire­ fringence, and hydrolytic degradation Reaction time and temperature played a key role to attain high DSacyl, although high reaction times at high temperature resulted in up to 16.2 % of the overall esterification with tartaric acid (DStar up to 0.5) 13C-SP-NMR, SEC-MALS-RI and the significant decreased of solubility in organic solvents, suggested that tartaryl groups participated in the formation of crosslinked di-starch tartrate, which seems logical considering the dihydroxy dicarboxylic nature of tartaric acid Acetylation significantly increased the hydro­ phobicity, thermal resistivity and processability (broader processing temperature) of pea starch Moreover, the use of organocatalyticallyacetylated pea starch with low DS (DSacyl ≤ 0.4) generated starchbased biofilms with higher tensile properties and lower water vapor permeability, whereas high DS (DSacyl ~ 2) increased the elongation at break of the films Low performance on acetylated pea starch with high DSacyl was attributed to the incompatibility between highly acetylated and native pea starches The efficient organocatalytic esterification process shown in this study resulted in pea starch acetate polymers with controlled degree of substitution that could serve to replace base-catalyzed acetylated starch esters typically used for food and biomaterial applications This com­ plementary mode of catalysis has enormous potential for savings in cost, time, and energy, resemble an easier experimental procedure, and reduce chemical waste Results from this study, together with the in­ clinations for clean labels, healthy eating, sustainability, and conve­ nience, could also fuel the growth of the global market for pea starch, with still unpaired abundance and demand Nonetheless, further studies would still be needed to investigate the compatibilization of tartaric acid catalyzed pea starch with other polysaccharides under scalable melt mixing (e.g., extrusion) to enhance interfacial adhesion and subsequent biomaterial properties Appendix A Supplementary data Supplementary data to this article can be found online at https://doi org/10.1016/j.carbpol.2022.119780 References Aburto, J., Alric, I., Thiebaud, S., Borredon, E., Bikiaris, D., Prinos, J., & Panayiotou, C (1999) Synthesis, characterization, and biodegradability of fatty-acid esters of amylose and starch Journal of Applied Polymer Science, 74, 1440–1451 https://doi org/10.1002/(SICI)1097-4628(19991107)74:6 Aˇckar, D., Babi´c, J., Jozinovi´c, A., Miliˇcevi´c, B., Joki´c, S., Miliˇcevi´c, R., Rajiˇc, M., & ˇ Subari´ c, D (2015) Starch modification by organic acids and their derivatives: A review Molecules, 20(10), 19554–19570 https://doi.org/10.3390/ MOLECULES201019554, 2015, Vol 20, Pages 19554-19570 Annison, G., Illman, R J., & Topping, D L (2003) Acetylated, propionylated or butyrylated starches raise large bowel short-chain fatty acids preferentially when fed to rats The Journal of Nutrition, 133(11), 3523–3528 https://doi.org/10.1093/JN/ 133.11.3523 ASTM 882-01 (2001) Designation "882-01, Standard test method for tensile properties of thin plastic sheeting." In Annual book of ASTM standards West Conshohocken, PA, USA: American Society for Testing Materials ASTM F1249-13 (2013) Standard test method for water vapor transmission rate through plastic film and sheeting using a modulated infrared sensor Annual book of ASTM standards West Conshohocken, PA, USA: American Society for Testing Materials ´ Avila Ramírez, J A., Cerrutti, P., Bernal, C., Errea, M I., & Foresti, M L (2019) Nanocomposites based on poly(lactic acid) and bacterial cellulose acetylated by an α-hydroxyacid catalyzed route Journal of Polymers and the Environment, 27(3), 510–520 https://doi.org/10.1007/S10924-019-01367-5/TABLES/2 ´ Avila Ramírez, J A., Fortunati, E., Kenny, J M., Torre, L., & Foresti, M L (2017) Simple citric acid-catalyzed surface esterification of cellulose nanocrystals Carbohydrate Polymers, 157, 1358–1364 https://doi.org/10.1016/J.CARBPOL.2016.11.008 ´ Avila Ramírez, J A., Suriano, C J., Cerrutti, P., & Foresti, M L (2014) Surface esterification of cellulose nanofibers by a simple organocatalytic methodology Carbohydrate Polymers, 114, 416–423 https://doi.org/10.1016/J CARBPOL.2014.08.020 Bello-P´ erez, L A., Agama-Acevedo, E., Zamudio-Flores, P B., Mendez-Montealvo, G., & Rodriguez-Ambriz, S L (2010) Effect of low and high acetylation degree in the morphological, physicochemical and structural characteristics of barley starch LWT - Food Science and Technology, 43(9), 1434–1440 https://doi.org/10.1016/J LWT.2010.04.003 Biliaderis, C G (2002) Physical characteristics, enzymic digestibility and structure of chemically modified smooth pea and waxy maize starches Journal of Agricultural and Food Chemistry, 30(5), 925–930 https://doi.org/10.1021/JF00113A029 Cano, A., Jim´enez, A., Ch´ afer, M., G´ onzalez, C., & Chiralt, A (2014) Effect of amylose: Amylopectin ratio and rice bran addition on starch films properties Carbohydrate Polymers, 111, 543–555 https://doi.org/10.1016/j.carbpol.2014.04.075 Clarke, J M., Topping, D L., Christophersen, C T., Bird, A R., Lange, K., Saunders, I., & Cobiac, L (2011) Butyrate esterified to starch is released in the human gastrointestinal tract The American Journal of Clinical Nutrition, 94(5), 1276–1283 https://doi.org/10.3945/AJCN.111.017228 Colussi, R., Pinto, V Z., El Halal, S L M., Biduski, B., Prietto, L., Castilhos, D D., … Dias, A R G (2017) Acetylated rice starches films with different levels of amylose: Mechanical, water vapor barrier, thermal, and biodegradability properties Food Chemistry, 221, 1614–1620 https://doi.org/10.1016/j.foodchem.2016.10.129 CRediT authorship contribution statement Natalia P Vidal: Investigation, Methodology, Formal analysis, Visualization, Writing – original draft Wenqiang Bai: Investigation, 11 N.P Vidal et al Carbohydrate Polymers 294 (2022) 119780 Mizuno, A., Mitsuiki, M., & Motoki, M (1998) Effect of crystallinity on the glass transition temperature of starch Journal of Agricultural and Food Chemistry, 46(1), 98–103 https://doi.org/10.1021/jf970612b Nielsen, T S., Bendiks, Z., Thomsen, B., Wright, M E., Theil, P K., Scherer, B L., & Marco, M L (2019) High-amylose maize, potato, and butyrylated starch modulate large intestinal fermentation, microbial composition, and oncogenic miRNA expression in rats fed A high-protein meat diet Int J Mol Sci., 20(9), 2137 https:// doi.org/10.3390/IJMS20092137, 2019, Vol 20, Page 2137 Nielsen, T S., Canibe, N., & Hofmann Larsen, F (2018) Butyrylation of maize and potato starches and characterization of the products by nuclear magnetic resonance and in vitro fermentation Foods, 7(5) https://doi.org/10.3390/foods7050079 Parandoosh, S., & Hudson, S M (1993) The acetylation and enzymatic degradation of starch films Journal of Applied Polymer Science, 48(5), 787–791 https://doi.org/ 10.1002/APP.1993.070480504 P´ erez, S., & Bertoft, E (2010) The molecular structures of starch components and their contribution to the architecture of starch granules: A comprehensive review Starch/ Staerke, 62(8), 389–420 https://doi.org/10.1002/star.201000013 John Wiley & Sons, Ltd Ragavan, K V., Hernandez-Hernandez, O., Martinez, M M., & Guti´ errez, T J (2022) Organocatalytic esterification of polysaccharides for food applications: A review Trends in Food Science and Technology, 119, 45–56 https://doi.org/10.1016/j tifs.2021.11.028 Elsevier Regulation (EC) No 1333/2008 (2008) Establishing common authorisation procedure for food additives, food enzymes and food flavourings Off J Eur Union, 354, 16–33 Ren, Y., Yuan, T Z., Chigwedere, C M., & Ai, Y (2021) A current review of structure, functional properties, and industrial applications of pulse starches for value-added utilization Comprehensive Reviews in Food Science and Food Safety, 20(3), 3061–3092 https://doi.org/10.1111/1541-4337.12735 Roman, L., Campanella, O., & Martinez, M M (2019) Shear-induced molecular fragmentation decreases the bioaccessibility of fully gelatinized starch and its gelling capacity Carbohydrate Polymers, 215, 198–206 https://doi.org/10.1016/j carbpol.2019.03.076 Saberi, B., Vuong, Q V., Chockchaisawasdee, S., Golding, J B., Scarlett, C J., & Stathopoulos, C E (2016) Mechanical and physical properties of pea starch edible films in the presence of glycerol Journal of Food Processing and Preservation, 40(6), 1339–1351 https://doi.org/10.1111/JFPP.12719 Sanyang, M L., Sapuan, S M., Jawaid, M., Ishak, M R., & Sahari, J (2015) Effect of plasticizer type and concentration on tensile, thermal and barrier properties of biodegradable films based on sugar palm (Arenga pinnata) starch Polymers, 7(6), 1106–1124 https://doi.org/10.3390/POLYM7061106, 2015, Vol 7, Pages 11061124 Schmidt, V C R., Blanco-Pascual, N., Tribuzi, G., & Laurindo, J B (2019) Effect of the degree of acetylation, plasticizer concentration and relative humidity on cassava starch films properties Food Science and Technology, 39(2), 491–499 https://doi org/10.1590/fst.34217 Shogren, R L (1996) Preparation, thermal properties, and extrusion of high-amylose starch acetates Carbohydrate Polymers, 29(1), 57–62 https://doi.org/10.1016/ 0144-8617(95)00143-3 Singh, J., Kaur, L., & McCarthy, O J (2007) Factors influencing the physico-chemical, morphological, thermal and rheological properties of some chemically modified starches for food applications—A review Food Hydrocolloids, 21(1), 1–22 https:// doi.org/10.1016/J.FOODHYD.2006.02.006 Singh, N., Chawla, D., & Singh, J (2004) Influence of acetic anhydride on physicochemical, morphological and thermal properties of corn and potato starch Food Chemistry, 86(4), 601–608 https://doi.org/10.1016/J FOODCHEM.2003.10.008 Thiebaud, S., Aburto, J., Alric, I., Borredon, E., Bikiaris, D., Prinos, J., & Panayiotou, C (1997) Properties of fatty-acid esters of starch and their blends with LDPE Journal of Applied Polymer Science, 65, 705–721 https://doi.org/10.1002/(SICI)1097-4628 (19970725)65:4 Tupa, M., Maldonado, L., V´ azquez, A., & Foresti, M L (2013) Simple organocatalytic route for the synthesis of starch esters Carbohydrate Polymers, 98(1), 349–357 https://doi.org/10.1016/j.carbpol.2013.05.094 Tupa, M V., Altuna, L., Herrera, M L., & Foresti, M L (2020) Preparation and characterization of modified starches obtained in acetic Anhydride/Tartaric acid medium Starch/Staerke, 72(5–6) https://doi.org/10.1002/star.201900300 ´ Tupa, M V., Avila Ramírez, J A., V´ azquez, A., & Foresti, M L (2015) Organocatalytic acetylation of starch: Effect of reaction conditions on DS and characterisation of esterified granules Food Chemistry, 170, 295–302 https://doi.org/10.1016/j foodchem.2014.08.062 Volant, C., Gilet, A., Beddiaf, F., Collinet-Fressancourt, M., Falourd, X., Descamps, N., Wiatz, V., Bricout, H., Tilloy, S., Monflier, E., Quettier, C., Mazzah, A., & RollandSabat´e, A (2020) Multiscale structure of starches grafted with hydrophobic groups: A new analytical strategy Molecules, 25(12) https://doi.org/10.3390/ molecules25122827 Xu, J., Andrews, T D., & Shi, Y C (2020) Recent advances in the preparation and characterization of intermediately to highly esterified and etherified starches: A review Starch/Staerke, 72(3–4) https://doi.org/10.1002/star.201900238 WileyVCH Verlag Xu, Y., Miladinov, V., & Hanna, M A (2004) Synthesis and characterization of starch acetates with high substitution Cereal Chemistry, 81(6), 735–740 https://doi.org/ 10.1094/CCHEM.2004.81.6.735 Commission Regulation (EU) No 231/2012 (2012) Specifications for food additives in Annexes II and III to Regulation (EC) No 1333/2008 of the European Parliament and of the Council Off J Eur Union, L 83/1 Cyras, V P., Zenklusen, M C T., & Vazquez, A (2006) Relationship between structure and properties of modified potato starch biodegradable films Journal of Applied Polymer Science, 101(6), 4313–4319 https://doi.org/10.1002/app.23924 Di Filippo, S., Tupa, M V., V´ azquez, A., & Foresti, M L (2016) Organocatalytic route for the synthesis of propionylated starch Carbohydrate Polymers, 137, 198–206 https:// doi.org/10.1016/J.CARBPOL.2015.10.039 Domínguez de María, P (2010) Minimal hydrolases: Organocatalytic ring-opening polymerizations catalyzed by naturally occurring carboxylic acids ChemCatChem, (5), 487–492 https://doi.org/10.1002/CCTC.201000030 El Halal, S L M., Colussi, R., Biduski, B., Evangelho, J A.d., Bruni, G P., Antunes, M D., … Zavareze, E.d R (2017) Morphological, mechanical, barrier and properties of films based on acetylated starch and cellulose from barley J Sci Food Agric., 97(2), 411–419 https://doi.org/10.1002/jsfa.7773 Ellingford, C., Samantaray, P K., Farris, S., McNally, T., Tan, B., Sun, Z., Huang, W., Ji, Y., & Wan, C (2022) Reactive extrusion of biodegradable PGA/PBAT blends to enhance flexibility and gas barrier properties Journal of Applied Polymer Science, 139 (6), 51617 https://doi.org/10.1002/APP.51617 Elomaa, M., Asplund, T., Soininen, P., Laatikainen, R., Peltonen, S., Hyvă arinen, S., & Urtti, A (2004) Determination of the degree of substitution of acetylated starch by hydrolysis, 1H NMR and TGA/IR Carbohydrate Polymers, 57(3), 261–267 https:// doi.org/10.1016/j.carbpol.2004.05.003 Food and Drugs Administration (FDA) (2017) Code of Federal Regulations (CFR), Title 21, Chapter Part 172- Food additives permitted for direct addition to food for human consumption Retrieved from https://www.accessdata.fda.gov/scripts/cd rh/cfdocs/cfcfr/CFRSearch.cfm?fr=172.892 Fundador, N G V., Enomoto-Rogers, Y., Takemura, A., & Iwata, T (2012) Syntheses and characterization of xylan esters Polymer, 53(18), 3885–3893 https://doi.org/ 10.1016/J.POLYMER.2012.06.038 Hadi, N A., Wiege, B., Stabenau, S., Marefati, A., & Rayner, M (2020) Comparison of three methods to determine the degree of substitution of quinoa and rice starch acetates, propionates, and butyrates: Direct stoichiometry, FTIR, and 1H-NMR Foods, 9(1) https://doi.org/10.3390/foods9010083 Huang, J., Schols, H A., Jin, Z., Sulmann, E., & Voragen, A G (2007a) Characterization of differently sized granule fractions of yellow pea, cowpea and chickpea starches after modification with acetic anhydride and vinyl acetate Carbohydrate Polymers, 67(1), 11–20 Huang, J., Schols, H A., Jin, Z., Sulmann, E., & Voragen, A G J (2007b) Pasting properties and (chemical) fine structure of acetylated yellow pea starch is affected by acetylation reagent type and granule size Carbohydrate Polymers, 68(3), 397–406 https://doi.org/10.1016/J.CARBPOL.2006.12.019 Huber, K C., & BeMiller, J N (2001) Location of sites of reaction within starch granules Cereal Chemistry, 78(2), 173–180 https://doi.org/10.1094/ CCHEM.2001.78.2.173 Huneault, M A., & Li, H (2007) Morphology and properties of compatibilized polylactide/thermoplastic starch blends Polymer, 48(1), 270–280 https://doi.org/ 10.1016/J.POLYMER.2006.11.023 Imre, B., García, L., Puglia, D., & Vilaplana, F (2019) Reactive compatibilization of plant polysaccharides and biobased polymers: Review on current strategies, expectations and reality Carbohydrate Polymers, 209(December 2018), 20–37 https://doi.org/10.1016/j.carbpol.2018.12.082 Imre, B., & Vilaplana, F (2020) Organocatalytic esterification of corn starches towards enhanced thermal stability and moisture resistance Green Chemistry, 22(15), 5017–5031 https://doi.org/10.1039/d0gc00681e Jane, J., Chen, Y Y., Lee, L F., McPherson, A E., Wong, K S., Radosavljevic, M., & Kasemsuwan, T (1999) Effects of amylopectin branch chain length and amylose content on the gelatinization and pasting properties of starch Cereal Chemistry, 76 (5), 629–637 https://doi.org/10.1094/CCHEM.1999.76.5.629 Kemas, C U., Ngwuluka, N C., Ochekpe, N A., & Nep, E I (2017) Starch-based xerogels: Effect of acetylation on physicochemical and rheological properties International Journal of Biological Macromolecules, 98, 94–102 https://doi.org/ 10.1016/j.ijbiomac.2017.01.101 Li, L., Yuan, T Z., Setia, R., Raja, R B., Zhang, B., & Ai, Y (2019) Characteristics of pea, lentil and faba bean starches isolated from air-classified flours in comparison with commercial starches Food Chemistry, 276, 599–607 https://doi.org/10.1016/J FOODCHEM.2018.10.064 L´ opez, O V., Lecot, C J., Zaritzky, N E., & García, M A (2011) Biodegradable packages development from starch based heat sealable films Journal of Food Engineering, 105 (2), 254–263 https://doi.org/10.1016/j.jfoodeng.2011.02.029 Luo, Z G., & Shi, Y C (2012) Preparation of acetylated waxy, normal, and high-amylose maize starches with intermediate degrees of substitution in aqueous solution and their properties Journal of Agricultural and Food Chemistry, 60(37), 9468–9475 https://doi.org/10.1021/jf301178c MacMillan, D W C (2008) The advent and development of organocatalysis Nature, 455 (7211), 304–308 https://doi.org/10.1038/nature07367, 2008 455:7211 Martinez, M M., & Boukid, F (2021) Future-proofing dietary pea starch ACS Food Science & Technology, 1(8), 1371–1372 https://doi.org/10.1021/ ACSFOODSCITECH.1C00219 Martinez, M M., Li, C., Okoniewska, M., Mukherjee, I., Vellucci, D., & Hamaker, B (2018) Slowly digestible starch in fully gelatinized material is structurally driven by molecular size and a and B1 chain lengths Carbohydrate Polymers, 197, 531–539 https://doi.org/10.1016/j.carbpol.2018.06.021 12 ... Determination of the degree of substitution of starch acetates (DSacyl) and the formation of starch tartrates (DStar) was done by calculating the ratio of the areas of the signal due to the carbon of the... diffraction angles 2θ of 15.1◦ , 17.1◦ , 18◦ , and 23◦ (Fig 3b) On one hand, organocatalytic acetylation did not alter the number and position of the diffraction peaks On the other hand, it resulted... Ramírez, J A., V´ azquez, A., & Foresti, M L (2015) Organocatalytic acetylation of starch: Effect of reaction conditions on DS and characterisation of esterified granules Food Chemistry, 170, 295–302