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TẠP CHÍ CÕNG TUNG ASSESSING THE EFFECTIVENESS OF CHEMICAL (NAOH) AND CELLULASE ENZYMATIC PEELING METHODS IN THE REMOVAL OF THE SKIN OF GRAPEFRUIT’CITRUS • LE PHAN THUY HANH TRAN QUYET THANG ABSTRACT F[.]
TẠP CHÍ CÕNG TUNG ASSESSING THE EFFECTIVENESS OF CHEMICAL (NAOH) AND CELLULASE ENZYMATIC PEELING METHODS IN THE REMOVAL OF THE SKIN OF GRAPEFRUIT’CITRUS • LE PHAN THUY HANH - TRAN QUYET THANG ABSTRACT: Fruit processing industry requires a convenient peeling method, especially during puree processing to prevent the deterioration of fruit quality and product loss In this study, manual, chemical (sodium hydroxide/NaOH) and enzymatic (Cellulase) peeling methods are selected to determine the effective peeling method for removing the skin of grapefruit’s citrus The study conducts experiments with Năm Roi grapefruit The effectiveness of different peeling methods changes in accordance with different peeling conditions, including concentrations (0.1-1.2% in the chemical peeling method, - 18% in the enzymatic peeling method), temperatures (70 - 80°C in the chemical peeling method, 50°C in the enzymatic peeling method), and soaking duration (30 - 120 seconds in the chemical peeling method, hours in the enzymatic peeling method) The results show that the optimal soaking time, temperature, and concentration for the chemical peeling method are 75 seconds, 75°c, and 0.8%, respectively Meanwhile, the enzymatic peeling method is not effective when the membrance of grapefruit’s flesh is still hard, and the membrance’s structure does not change Keywords: chemical (NaOH) peeling, cellulase enzymatic peeling, enzyme cellulase, Năm Roi grapefruit, peeling of grapefruit’s flesh Introduction Peeling is performed before further process it as fruit-based products (Srikaeo et al., 2011; Rock et al., 2012) In addition, Srikaeo et al., (2011) also stated that the processing of any fruit-based products, it is important to minimize the loss of yield while retaining the quality of the products through ideal peeling methods On the other hands, the peeling process often results in yield losses unless the concentrations, the temperature, the time in the peeler are controlled (Garcia et al., 2006) Various peeling methods have been utilized, including the use of hand/manual or mechanical, 142 So 15-Tháng 6/2022 steam or hot, lye or chemical, and enzymes (Rock et al 2011; Li, 2012) Chemical peeling using sodium hydroxide (NaOH) is also one of the most common methods used besides manual, for peeling of fruit and vegetables (Garcia et al., 2006) Furthermore, the chemical peeling is more preferred and widely applied among manufacturers due to its association with higher product yields and better product quality compared to manual peeling (Rock et al., 2012) However, Rock et al., 2012 also showned that large amount of water are required for washing stage which has caused severe damage to the envứonment due to the discharge of NaOH used during peeling HĨA HỌC-CƠNG NGHỆ THựC PHẨM process Therefore, enzymatic peeling was used as an alternative for chemical peeling Grapefruit is a fruit that many people enjoy because it not only is used to quenches durst very good but also has preventive and curative effects In addition to the common chemical components such as sugar, minerals, organic acids, grapefruit also contains a lot of galacturonic acid, vitamin c, pectin, phenol, flavoinoids (limonoid, hesperidin and naringin) , which have antioxidant effects very strong, helps to slow down the aging and damage of cells, protect the elasticity of blood vessels, prevent arteriosclerosis, indirectly against high blood pressure and cerebrovascular accident, reduce the risk of heart failure and cancer (Shirou et al., 2010; Caitlin et al., 2012) In addition, grapefruit also has many beauty uses such as helping to keep the skin healthy and youthful, resisting the attack of envứonmental pollutants, helping the epidermis to balance nutritional factors and lose weight quickly (Caitlin et al., 2012) Grapefruit requires skin peeling before further processes Therefore, alternative methods using chemical and enzymatic peeling can be used for efficient peeling in separating the skin The relationship between the variables (temperature, concentration, peeling time and grapefruit’s citrus characteristics) is critical to avoid high loss of pulp from over peeling This study aims to determine the peeling efficiency of grapefruit’s citrus using alternative methods (chemical and enzymatic peeling) compared to the conventional method (manual peeling) Materials and methods 2.1 Raw materials The raw material is Năm Roi grapefruit with an average weight of 1.1 - 1.3 kg, round fruit, slightly tapered fruit’s head, uniform ripeness, slightly yellow skin, intact fruit, not rotting or damaged, or any damage caused by insects, no strange odor or taste and hard fruit (R J Nissen, Nguyen Duy Due, Nguyen Minh Chau, and et al., 2008) Enzyme Cellulase 1.5L is made in Denmark, optimal conditions for enzyme activity are pH 4.5 6.0 and temperature 50 - 60°C, stored at low temperature (5 - 10°C) Alkali (NaOH) is made in Taiwan, white solid, purity: 96%, easily soluble in water 2.2 Experimental design Analyses method Sensory method Experimental design The research stages are designed according to Figure After receiving raw materials, the grapefruits were washed to remove dirt before further peeling process After that, the grapefruits were transferred to the stage of stem separation and classification, and continue to be blanched in hot water at 100°C for 10 minutes in order to soften the outer skin so that it can be easily removed After the heat treatment, the grapefruits were transferred to separating the skin of the grapefruit’s citrus by Chemical (NaOH) peeling and Cellulase enzymatic methods The treatmented products are evaluated for sensory method for separation of the skin of the grapefruit’s citrus and the structure of grapefruit’s cloves Follow the steps shown in Figure to separate the skin of the grapefruit’s citrus, Preliminary studies was carried out about: Experiment 1: Chemical (NaOH) peeling The change the peeling concentration from 0.1 to 1.2% at a temperature of 70°C with time Of minute was studies Next, surveyed temperature with the selected peeling concentration from the above experiment at the peeling time of minute was carried out on different ranges of temperature (70'C, 72°c, 74°c, 76°c, 78°c, 80°C, etc.) In the end, surveyed time with a selected peeling concentration and time from the above experiment was carried out on different ranges of time (30 to 120 seconds) Experiment 2: Cellulase enzymatic peeling Cellulase enzyme has optimal pH of about 4.5 - So, chosen pH to peel was In addition, the best temperature for Cellulase Enzyme is from 50 - 60°C, so the temperature was chosen at 50°C to study The optimal concentration was surveyed by changing the concentration (1%, 2%, 3%, 4%, 5%, etc.) at the peeling time of hours Data analysis All experiments were repeated times SPSS software was used to find out the difference between the experiments through ANOVA and LSD treatment Graphs are drawn using Microsoft Excel software Results and discussion 3.7 Experiment 1: Chemical (NaOH) peeling 3.1.1 Peeling concentration The using of the lye in the fruit and vegetable peeling has been widely applied Depending on the SỐ 15-Tháng Ó/2022 143 TẠP CHÍ CƠNG THƯƠNG type of fruit and vegetable, the peeling concentration, temperature and time are different The results of the lye concentration survey are shown in Table From the results of Table 1, show that the higher concentration of alkaline solution, the skin of the grapefruit’s citrus are faster corroded This can be explained based on Pagn et al (2005 and 2010), the industrial processes for peeling consist of manual skin removal and further chemical degradation of pericarp (skin) and mesocarp (flesh) of the fruits This method removes the cuticle and some of the most external cell layers of fruits Once the chemical (lye or caustic) solution is in contact with pericarp (skin) of the fruits, the epicuticular waxes are dissolved and the NaOH penetrates the epidermis and diffuses through the skin into the mesocarp (flesh) of fruit and, thus, separates the skin When the concentration of alkaline solution is high, the diffusion rate and the reaction rate is faster (J D Floros and M s Chinnan, 1990) In contrast, when the concentration of NaOH is low, there is an effect on diffusion due to the chemical reactions occurring during the diffusion process Inside skin of the grapefruit’s citrus contains many compounds, 144 SỐ 15 - Tháng Ó/2022 NaOH will react with these substances and macromolecules (polygalacturonic acid, other organic acids, hemicellic polysaccharides, proteins, etc.) These reactions occur to slow the diffusion of NaOH At low NaOH concentrations, the processing time for skin of the grapefruit’s citrus will be longer (J D Floros and M s Chinnan, 1990) Therefore, when increasing the concentration of NaOH solution during the treatment of skin of the grapefruit’s citrus, the hydrolysis efficiency will increase gradually However, the higher the concentration, the structure of grapefruit’s citrus is softer Because the skin of the grapefruit’s citrus is only eroded with a certain amount of alkaline solution When it is completely eroded, the residual alkaline solution will dừectly impact on the grapefruit’s citrus, causing the links in the structure of the grapefruit’s citrus to be broken To be able to solve the two problems of peeling the peel and ensuring the structure of the grapefruit grapefruit’s citrus, the optimal concentration is 0.8% 3.1.2 Peeling temperature The temperature of NaOH solution is commonly used to soaking citrus fruits or other fruits (mango, potato, tomato, etc.) is 70 - 95°c or HĨA HỌC-CƠNG NGHỆ THựC PHẨM Table The influence of the lye concentration to separating the skin of the grapefruits’s citrus Concentration 0.1% Result (70°C, the time of minute) The skin of the grapefruit’s citrus is still normal, no been corroded The structure of grapefruit’s cloves is normal and unchanged The skin on both sides of the grapefruit’s citrus begin to be corroded, the back and abdomen of the 0.3% grapefruit’s citrus have not been corroded, the veins on the grapefruit’s citrus are hard The structure of grapefruit’s cloves is normal and unchanged The skin on both sides of the grapefruit’s citrus are corroded, the abdomen of the grapefruit’s citrus are 0.5% corroded but the back of the grapefruit’s citrus have not been corroded, the veins on the grapefruit’s citrus are hard The structure of grapefruit’s cloves is normal and unchanged 0.7% 0.8% 0.9% 1% 1.2% The skin of the grapefruit’s citrus is corroded, the veins on the grapefruit’s citrus are soft The structure of grapefruit’s cloves is normal and unchanged The skin of the grapefruit’s citrus is corroded, the veins on the grapefruit’s citrus are soft and separate easily The structure of grapefruit’s cloves is normal and unchanged The skin of the grapefruit’s citrus is corroded, the veins on the grapefruit’s citrus are soft and separate easily The structure of grapefruit’s cloves is normal and unchanged The skin of the grapefruit’s citrus is corroded, the veins on the grapefruit's citrus are soft and separate easily The structure of grapefruit’s cloves begins to be soft The skin of the grapefruit’s citrus is completely corroded The structure of grapefruit’s cloves is changed, it becomes very soft higher (N s Mohamad and et al., 2017) Therefore, the survey will be carried out at the temperatures of 70°C, 72°c, 74°c, 76°c, 78°c, 80°C with the selected peeling concentration from the above experiment at the peeling time of minute The results of the processing temperatures are presented in Table From the results of Table 2, it shows that, when the temperature is increased from 70 - 75°c, the NaOH treatment efficiency is more increases, but when the temperature is over 75°c, although the separation efficiency is easy, it affects the structure of grapefruit cloves, peeled grapefruit’s cloves As when the temperature is increases, the diffusion and reaction from NaOH will increase to make the easily separated skin but when the temperature is too high then the rate of diffusion and reaction of NaOH are stronger, affects the whole grapefruit’ cloves causing soft Therefore, the most optimal temperature for alkali treatment is 75°c 3.1.3 Peeling time The peeling time is related to the diffusion and reaction of NaOH solution on the skin and cloves of the grapefruit’s citrus The increasing time, the NaOH solution has time to diffuse and react, the skin and cloves of the grapefruit’s citrus is separated easily But when the time is too long, the NaOH solution diffuses and reacts with the whole grapefruit’s cloves The structure of grapefruit’s membrance is changed, it become very soft The survey results of the treatment time with NaOH solution are shown in Table According to the results of Table 3, when increasing the time from 30 to 75 seconds, the separation efficiency of the skin of the grapefruit’s citrus increases, the skin of the grapefruit’s citrus is easily separated and does not affect the structure of grapefruit’s cloves However, when the time is over 75 seconds, it is easier for the the skin of the grapefruit’s citrus to be separated, but at the same time, the structure of grapefruit’s cloves is also affected, and the grapefruit’s cloves are disintegrated Therefore, the optimal time for alkaline treatment is 75 seconds SƠ'15-Tháng 6/2022 145 TẠP CHÍ CƠNG THƯƠNG Table The influence of the lye temperature to separating the skin of the grapefruit’s citrus Result (concentration of 0.8%, the time of minute) Temperature The skin of the grapefruit’s citrus is corroded, the veins on the grapefruit’s citrus are soft and separate 70°C easily but there are some veins and skin on the grapefruit’s citrus The structure of grapefruit’s cloves is normal and unchanged The skin of the grapefruit’s citrus is corroded, the veins on the grapefruit’s citrus are soft and separate 72°c easily but there are some veins and skin on the grapefruit’s citrus The structure of grapefruit’s cloves is normal and unchanged The skin of the grapefruit’s citrus is corroded, the veins on the grapefruit’s citrus are soft and separate 74°c easily but there are some veins and skin on the grapefruit’s citrus The structure of grapefruit’s cloves is normal and unchanged The skin of the grapefruit’s citrus is corroded, the veins on the grapefruit's citrus are soft and separate easily 75°c The structure of grapefruit’s cloves is normal and unchanged The skin of the grapefruit’s citrus is corroded, the veins on the grapefruit’s citrus are soft and separate easily 76°c The structure of grapefruit’s cloves begins to be soft The skin of the grapefruit’s citrus is completely corroded 78°c The structure of grapefruit’s cloves is changed, it become very soft The skin of the grapefruit’s citrus is completely corroded 80°C The structure of grapefruit’s cloves is changed, it become very soft Table The influence of the lye time to separating the skin of the grapefruit’s citrus Time Result (concentration of 0.8%, temperature of 750C) The skin on both sides of the grapefruit’s citrus begins to be corroded, the back and abdomen of the 30 seconds grapefruit’s citrus have not been corroded, the veins on the grapefruit’s citrus are hard The structure of grapefruit’s cloves is normal and unchanged 45 seconds The skin of the grapefruit’s citrus is corroded, the veins on the grapefruit’s citrus are soft and separate easily but there are some veins and skin on the grapefruit’s citrus The structure of grapefruit's cloves is normal and unchanged The skin of the grapefruit's citrus is corroded, the veins on the grapefruit’s citrus are soft and separate easily 60 seconds but there are some veins and skin on the grapefruit's citrus The structure of grapefruit’s cloves is normal and unchanged 75 seconds 90 seconds 100 seconds 120 seconds The skin of the grapefruit’s citrus is corroded, the veins on the grapefruit's citrus are soft and separate easily The structure of grapefruit’s cloves is normal and unchanged The skin of the grapefruit’s citrus is completely corroded The structure of grapefruit’s cloves is changed, it becomes soft The skin of the grapefruit’s citrus is completely corroded The structure of grapefruit’s cloves is changed, it becomes very soft The skin of the grapefruit’s citrus is completely corroded The structure of grapefruit’s cloves is changed, it becomes very soft 146 SƠ 15 - Tháng Ĩ/2022 HĨA HỌC-CƠNG NGHỆ THựC PHẨM 3.2 Experiment 2: Cellulase enzymatic peeling Enzymatic peeling is performed by treating the fruit with a high activity enzymatic solution containing polysaccharide hydrolytic enzymes, especially pectinases, cellulases, and hemicellulases since pectin, cellulose and hemicellulose are the polysaccharides that are responsible for the adherence of the skin to the flesh The results showed that pectinases and cellulases were the enzymes that led to a more efficient peeling process (Pagan et al., 2005; Pagan et al., 2010) The principle of enzymatic peeling is based on the digestion, through an enzymatic preparation, of the pectic substances existing in the cell wall of plants (R E Berry, R A Baker, and J H Bruemmer, 1988) Cellulases are prob- ably necessary for the release of pectins in the albedo and pectinases complete the process by contributing to the hyd-rolysis of polysaccharides making up the cell wall (A Rouhana and c H Mannheim, 1994) However, after conducting an experiment to investigate the concentration, the effective level of using enzymes in separating the skin of the grapefruit’s citrus is not effective, even though the safety of the enzyme method is higher than that of the alkaline method, specifically, conducted enzyme survey at pH of 5, time of hours, temperature of 50°C with different concentrations, the results are shown in Table Experimental survey results at enzyme concentrations from -18% was carried out many times but did not bring results, the citrus peel was still hard, there was no soft, the percentage of peel which was corroded very small, almost no yes, the structure hasn't changed much It could be due to many different reasons In addition to the kind of enzymatic preparation used, there are numerous parameters that affect the quality of the finished product and successful peeling Among them, the morphologic characteristics of fruits, such as skin adherence and its thickness and the unity rate between segments, are important factors which determine enzymatic peeling efficiency (Pretel et al., 2001) The porosity of the citrus albedo varies with the species and the variety Therefore, is an important parameter to take into account when a suitable vacuum is selected, since the vacuum should be more intense when the albedo is not very porous Table The influence of Cellulase enzyme concentration to separating the skin of the grapefruit’s citrus (Pretel et al 2005) Likewise, the capacity of the fruit skin to absorb the enzyme solution depends on peel thickness (Pretel et al., 2007a, 2007b) However, not all citrus fruits are amendable to obtain segments through enzymatic peeling, since some morphological characteristics such as the compression of the albedo or the fragility of the segment peel could hinder this process If only the entire peeled citrus is needed, the most important parameter to consider is the adherence rate of the albedo to the segments Other critical parameters include the presence of the navel, the adherence between segments and the homogeneity of the membrane (Pretel et al., 2007a, 2007b) In addition to all the factors directly concerning enzymatic peeling, other indirect factors such as the ripening stage can influence the ease of enzymatic peeling of citrus Throughout the ripening process a series of irreversible physical, biochemical and physiological changes are brought about in the fruits, which included breathing intensity, colour changes, increase in sugar content and decrease in firmness (Serrano et al 2005) Among these changes, the enzymatic degradation of the glucidic polymers increases, in particular the pectin and hemicellulose substances, weakening So 15 - Tháng Ĩ/2022 147 TẠP CHÍ CƠNG THƯƠNG the cell wall and their disposition (Brady, 1987) More importantly, the behaviour of the enzymes during the degradation of the cell walls is influenced by the physical and chemical properties of the plants, which can vary from one species to within the same variety, during the another, or even ripening process (Ismail et al 2005) Conclusion Chemical (NaOH) peeling and Cellulase enzymatic peeling of grapefruit’s citrus was carried out The results show that, the skin of peeled alkaline solution (NaOH) with a concentration of 0.8% solution, temperature of 75°c, processing time of 75 seconds The biological method of separating skin grapefruit’s citrus is by enzyme) of grapefruit’s citrus (using Cellulase was not effective at enzyme concentrations from Ito 18% ■ REFERENCES: A Rouhana and c H Mannheim (1994) Optimization of enzymatic peeling of grapefruit LWT - Food Science and Technology, 27, 103-107 Brady CJ (1987) Fruit ripening Annual Review of Plant Physiology, 38, 155-178 Caitlin, A.D., B Scott, s.c Hsiao-Hui, s.p Bhimanagouda, A.T Cynthia (2012) The effects of daily consumption of grapefruit on body weight, lipids, and blood pressure in healthy, overweight adults Clinical Science, 61(7), 1026-1035 Ismail M A, Chen H, Baldwin EA, Plotto A (2005) Changes in enzyme-assisted peeling efficiency and quality of fresh ‘Valencia’ orange and of stored ‘Valencia’ orange and ‘Ruby red’ grapefruit Proceedings of the Florida State Horticultural Society, 118,403-405 J D Floros and M s Chinnan (1990) Diffusion Phenomena during Chemical (NaOH) Peeling of Tomatoes Journal ofFood Science, 55(2), 552-553 Li, X (2012) A study of infrared heating technologyfor tomato peeling: Process characterization and modelling Davis: University of California, PhD thesis N s Mohamad and et al (2017) Comparison between conventional and alternative peeling methods on peeling efficiencies of Malaysian 'Chok Anan' mango (Mangifera indica L.) fruit International Food Research Journal, 24(5), 1934-1940 Pagn, A., Conde, J., Ibarz, A and Pagn J (2010) Effluent Content from albedo degradation and kinetics at different temperatures in the enzymatic peeling of grapefruits Food Bioproduct Process, 88,77-82 Pagan, A., Ibarz, A and Pagn, J (2005) Kinetics of the digestion products and effect of temperature on the enzymatic peeling process of oranges Journal of Food Engineering, 71 (4), 361 -365 10 R E Berry, R A Baker, and J H Bruemmer (1988) Enzime separated sections: A new lighly proccessed citrus product Proceedings of the 6th International Citrus Congress, Tel-Aviv, Israel) Philadelphia: Balaban Publishers, 1711-1716 11 Garcia, E and Barrett, D M (2006) Evaluation of processing tomatoes from two consecutive growing seasons: Quality attributes, peelability and yield Journal of Food Processing and Preservation, 30,20-36 12 Rock, c., Yang, w., Goodrich-Schneider, R and Feng, H (2012) Conventional and Alternative Methods for Tomato Peeling Food Engineering Reviews, 4(1), 1-15 13 Pretel MT, Amorĩs A, Botella MA, Serrano M, Romojaro F (2005) Study of albedo and carpelar membrane degradation for further application in enzy - 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