The objectives of this study were: 1 to exam the effect of three market types and two sampling times on off-odors/off-flavors in beef in Vietnam; 2 to exam the effect of two above factor
INTRODUCTION
Meat is a complex matrix which is a highly nutritious food, rich in proteins, amino acids, vitamins (vitamin A, C, E; especially vitamin B complex), and minerals (zinc and iron), hence it is highly perishable Lipids are vital components of meat, which plays important role in consumer’s acceptance reflecting several desirable characteristics of meat such as color, flavor, tenderness, and juiciness The presence of oxygen and metals such as iron may be brought about by a high intake of oxidized lipids or polyunsaturated fatty acids (Olsen et al., 2005) Furthermore, lipid oxidation is one of the most important factors that affect the quality of meat, especially in beef meat Many volatile compounds such as aldehydes were formed, which are responsible for off-odor (Ahn et al., 1998, Ahn and Lee, 2002), off-flavor (Dietze et al., 2007) and rancidity (Campo et al., 2006; Ahn et al., 2002; Byme et al., 2002), and change meat color (Guillen-Sans and Guzman-Chozas, 1998) Lipid oxidation can occur in both fresh and cooked meats (Min and Ahn, 2005; Jo et al., 2006)
In addition, other factors also play different roles in the change of meat quality that is strongly linked to microorganisms, especially in case of the meat displayed in the market The microbiological quality of meat depends on the physiological status of the animal at slaughter, the spread of contamination during slaughter and processing, the temperature and other conditions of storage and distribution In fact, some of the microorganisms originate from the animal’s intestinal tract as well as from the environment with which the animal had contact at some time before or during slaughter (Koutsoumanis and Sofos, 2004) E coli, coliforms, and aerobic plate count are indicators of fecal contamination, environmental contamination, and overall hygienic conditions
Raw meat is associated with intrinsic antioxidants such as α-tocopherol (vitamin E), β- carotene (vitamin A), ascorbic acid (vitamin C), glutathione, and antioxidant enzymes (glutathione peroxidases, superoxide, dismutases and catalase) These compounds retard lipid oxidation in fresh and stored meat, and preserve the beef color and beef odor quality as well The antioxidants are incorporated within cell membranes and protect tissues against oxidation from reactive oxygen species This maintains the overall quality of meat and secondary products The antioxidant potential in meat is determined by the antioxidant composition and the antioxidative properties of constituents By definition, the antioxidant activity (AOA) is the capability of a compound to inhibit oxidative degradation, e.g lipid peroxidation The antioxidant capacity gives information about the duration of antioxidative action, the reactivity characterizes the starting dynamics of antioxidation at a certain concentration of an antioxidant or antioxidant mixture Individual antioxidants can react as chain-braking of oxidative reactions and the activity is related to the reactivity of the antioxidants to free radicals (Roginsky and Lissi, 2005) Recently, researchers have been interested in the methods for determining total antioxidant capacity from raw meat (Abu-Salem et al., 2014; Gatellier et al., 2004) The authors have developed the different measurement methods, including Ferric Reducing Antioxidant Power (FRAP) method (Benzie and Strain, 1996; Pulido, Bravo, and Saura-Calixto, 2000), Trolox Equivalent Antioxidant Capacity (TEAC) method (Re et al., 1999), and Folin-Ciocalteu (FC) method (Stratil et al., 2006; Lee et al., 2014) Besides, Sứrensen and Jứrgensen, (1996) has developed Thiobarbituric Acid Reactive Substances (TBARS) method to determine secondary oxidation products such as carbonyls (ketones and aldehydes), alcohols, hydrocarbons (alkane, alkene), and furans
Many factors impact on the development of lipid oxidation in fresh meat such as external factors and internal factors The internal factors include fat conten, fatty acid composition, and antioxidants, heme pigments and iron content (Addis, 1986; Du et al., 2000; Choe and Min., 2006; Min et al., 2008), and metal catalysts and degree of polyunsaturation in the lipids of meat play the most important roles (Gray and Pearson, 1987; Calkins and Hodgen 2007) The external conditions such as processing, environmental factors, exposure time of raw meat without package, packaging (Kumar et al., 2015; Esmer et al., 2011; Khairy 2010) and stogage conditions also considerably contribute to lipid oxidation process (Ahn et al., 2009) temperature and sunlight play a major important part on the lipid oxidation development
The objectives of this study hence are: 1) to exam the effect of three market types and two sampling times on off-odors/off-flavors in beef in Vietnam; 2) to exam the effect of two above factors on the lipid oxidation through two indicators known as total antioxidant capacities and secondary products of oxidation; and 3) to evaluate the counts of aerobic bacteria quantity grown on meat surface affected by different market types and sampling times
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EFFECTS OF MARKET SETTING AND TIME OF PURCHASE ON OFF-ODOR AND OFF-FLAVOR DESCRIPTORS IN BEEF (Longissimus Muscle)
EFFECTS OF MARKET SETTING AND TIME OF PURCHASE ON OFF- ODOR AND OFF-FLAVOR DESCRIPTORS IN BEEF ( Longissimus Muscle) IN
Phuong T T Vu 1 , April K McCain 2 , Tran H B Cao 1 , Cam T H Tran 3 , Man V V Le 1 ,
Dung H Nguyen 1 , and Thu T N Dinh 2
1Chemical Engineering, HCMC University of Technology, Ho Chi Minh City, Vietnam
2Animal and Dairy Sciences, Mississippi State University, Mississippi State, Mississippi,
3Faculty of Food Technology, HCMC University of Food Industry, Ho Chi Minh City,
Beef quality is an important driver of purchase decision by Vietnamese consumers
This study was to evaluate the influence of type of markets, and time of purchase on the sensory quality of beef across three regions of Vietnam
Beef Longissimus muscle samples were collected in Ha Noi, Da Nang, and Ho Chi
Minh City to represent regional variation in meat mechandizing in Vietnam Five beef samples were randomly purchased at each of two open markets (OM), two indoor markets (IM), and two supermarkets (SM) in each region at the opening of the markets (T0) and 4 h after the opening (T4) Beef samples were evaluated for raw and cooked descriptive off-odors by trained panelists The descriptive panel was trained to identify, define, and evaluate the intensity of raw livery, raw sweet, raw sour, cooked livery, and cooked sour odors on a 6-point scale (0 = totally lacking; 5 = very intensive) A generalized linear mixed model was used to analyze the variances with market type, sampling time, and their interaction as fixed effects and region as a random effect in a randomized complete block design Statistical significance was determined at P ≤ 0.05
There was no treatment effect (P ≥ 0.090) on raw sweet odor and cooked sour flavor
Market type significantly influenced raw livery odor (P = 0.013) Beef samples from OM developed less raw livery odor than beef from IM (P = 0.004) Whereas raw livery odor in beef from SM did not differ from that in beef from OM and IM (P 0.061 and 0.292, respectively) Beef samples at T0 had less raw sour odor and cooked livery flavor than those at T4 (P = 0.019 and 0.032, respectively)
These results indicate that raw livery odor varied by market types In addition, raw sour and cooking livery odors increased as beef was purchased later in the day (T4 vs
T0) The findings of this study provided useful information to predict purchase decision by beef consumers and to devise a strategy to manage beef quality at various markets in Vietnam
Keywords : beef quality, Longissimus muscle, odor, descriptive, sensory quality
Sensory evaluation is the multidisciplinary approach using human senses as instruments for assessing food quality In terms of qualitatively and quantitatively assessing a food using trained panels, it is referred to descriptive test (1992, 1992)
The beef quality is a complex concept assessed based on consumer requirements and acceptance It is defined by sensory attributes, instrumental and chemical attributes of beef (Spanier et al., 1992), (Cardello, 1995), (Molnár, 1995) Beef sensory attributes include three main groups: flavor (e.g., aroma, taste), texture (e.g., tenderness, juiciness), appearance (e.g., color, appeal, size) (Molnár, 1995), (St Angelo, 1996)
(Stelzleni and Johnson, 2008), (Calkins and Hodgen, 2007) showed that flavor is a very complex attribute to be used to define taste and aroma
The flavor of beef depends on factors such as diet (Shahidi, 1986), (Sitz et al., 2005), the polyunsaturated fats content (PUFAs) (Baublits et al., 2009), the post-mortem aging period (Sitz et al., 2005), (Spanier et al., 1997), (Ba et al., 2014), and end-point cooking temperature (Spanier and Miller, 1996)
Besides, (St Angelo, 1996) showed that the basic chemical reactions focusing on lipid oxidation had impact on beef flavor quality through chemical analysis by the TBA test and sensory analysis by descriptive panel (Gray et al., 1996) also described that lipid oxidation is one of the important periods of quality deterioration in beef samples and further stated that the negative characteristics of changes in quality were the indicators of the off-flavor formations Besides, (Gray, 1987), (Gray et al., 1996), (Campo et al., 2006), (Hansen, 2007), (Khan, 2014) pointed out that lipid oxidation was one of the main causes that affected beef sensory quality by forming off-flavors and off-odors
Furthermore, the previous studies (Savell et al., 1987), (Spanier and Miller, 1996), (Robbins et al., 2003) showed that off-flavors were fully reflected the beef quality and was one of the significant factors affecting consumer purchasing decisions
Meat packing such as modified atmospheric packaging (MAP), vacuum packaging (VP), control atmosphere packaging (CAP) protects meat from external effects as concentrated CO 2 , O 2 , level of surface exposure to atmosphere which are the major causes of lipid oxidation In addition, the environmental conditions as sunlight, temperature, humidity, display condition also affected lipid oxidation Some previous studies indicated that packing process effected on level of exposure (Spanier et al., 1992), package type (Khan, 2014)
In Vietnam, fresh meat is displayed at supermarket (SM) in expanded polystyrene tray wrapped PVC film at refrigerated temperature (0 – 4 0 C) At indoor market (IM) and open market (OM), raw materials are directly exposed of sunlight, in varied temperature without being packed Moreover, taste and aroma is one of the most important sensory traits affecting acceptance of comsumer (Robbins et al., 2003), (Kerth et al., 1995), Feuz et al., 2004)
Therefore, it is important to investigate the market type and display conditions impacted on meet flavor The objective of this study found out the influence of market type and display time on sensory beef quality across three regions of Vietnam through off-odor and off-flavor descriptors
Meat samples for training were obtained from local grocery stores in Ho Chi Minh City (HCMC) Those for the final experiment were obtained from the three representative regions of Vietnam, HCMC, Da Nang (DN), and Ha Noi (HN) The three types of markets (supermarket (SM), indoor market (IM), and open market (OM)) were classified according to their characteristics (the availability of refrigeration, the availability of air conditioning, and the architectural exterior of the markets such as walls and roofs (Table 2.1)
Table 2.1 Characteristics used to classify supermarkets (SM), indoor markets (IM), and open markets (OM) across three regions of Vietnam
In each market type, the number of markets was two that resulted in six markets per region Two sampling times were selected to collect samples at each market The opening time (T0) was individually selected corresponding to the opening schedule of individual markets and the closing time (T4) was 4 h after the opening Longissimus muscle was chosen for use in this study Five 300-g Longissimus muscle samples were collected aseptically from various vendors, so there were 180 samples Vendors were randomly selected when sampling If a market had less than five vendors, at least one vendor was sampled repeatedly in the rotating order There was no vendor choice in the SM because each SM was the only meat vendor Those samples were purchased separately and from different sub-primals At T4, in general, samples were purchased again at the original vendors selected at T0 The vendor randomization process was executed in the similar manner The samples were placed isolatedly in zip plastic bags and were coded with ―B‖ for ―beef‖ and three-digit number from 001 to 180 The bags were zipped immediately after meat was put Samples were stored in the Igloo Super Tough Sportsman ice chest (Igloo, Katy, TX) with ice packs
Beef samples in the ice chests were transported back to a local university in each region After vacuum-packed by a household vacuum machine (DZ 300A), the samples were immediately stored at -20 0 C in a freezer (Sanaky VH365A1 in HCMC, Sanyo MDF-U333 in DN, or Alaska HB 490 490L in HN) until ready to be evaluated
The samples were removed from the freezer 24 h prior to cook and allow to thaw in the refrigerator (4 0 C) (Adhikari et al., 2011) Samples for both training and the final experiment were prepared in the same procedure The samples were cut into equally two parts of which the piece for fresh sample test is approximately 50-g and the piece for cooked is approximately 250-g
To raw fresh samples test, samples were milled by grinder (Pensonic Grinder PB- 6000) and put into dark glass jars coded with random three-digit numbers The panel only evaluated samples when the samples were inside the jars at least 5 mins
EFFECTS OF MARKET SETTING AND TIME OF PURCHASE ON
EFFECTS OF MARKET SETTING AND TIME OF PURCHASE ON THE TOTAL ANTIOXIDANT CAPACITY (TAC) AND THIOBARBITURIC ACID REACTIVE SUBSTANCES (TBARS) VALUE OF BEEF ( Longissimus Muscle)
Phuong T T Vu 1 , April K McCain 2 , Man V V Le 1 , Dung H Nguyen 1 , and Thu T N
1Chemical Engineering, HCMC University of Technology, Ho Chi Minh City, Vietnam
2Animal and Dairy Sciences, Mississippi State University, Mississippi State, Mississippi,
In this study, the total antioxidant capacity (TAC) of intrinsic antioxidants in beef was measured by three different analytical methods: Folin-Ciocalteu (FC) method, Trolox equivalent antioxidant capacity (TEAC) method using 2,2’-azino-bis-(3- ethylbenzothiazoline-6-sulfonic acid) (ABTS+) radical cationdecolourisation, and ferric reducing antioxidant power (FRAP) method Trolox had been used as a standard reagent Moreover, this study investigated the products of lipid oxidation through using thiobarbituric acid reactive substances (TBARS) TBARS values of beef samples collected from supermarket (SM) were the highest compared to those of the samples from indoor market (IM) and open market (OM) (P ≤ 0.05) FC method indicated the significant effect of market type and display time on TAC of intrinsic antioxidants In both the FC and TEAC methods, OM had the highest TAC compared to IM and SM (P ≤ 0.05) Display time T4 showed the highest TAC value in FC method (P ≤ 0.05) The result of this study demonstrated that market type and display time of beef affected significantly on beef quality
The total antioxidant capacity (TAC), Folin-Ciocalteu (FC) method, Trolox equivalent antioxidant capacity (TEAC) method, Ferric reducing antioxidant power (FRAP) method, Thiobarbituric acid reactive substances (TBARS)
The antioxidant activity of a compound is an ability to reduce pro-oxidants which cause or promote the oxidation Many analytical methods have been developed to determine the antioxidant activity (TAA), total antioxidant capacity (TAC) in all kinds of food, including beverages (Schlesier et al 2002), vegetables (Stratil, Klejdus and Kubáň 2006), meat (Abu-Salem et al 2014) and fruits (Alothman, Bhat and Karim 2009), (Thaipong et al 2006), cocoa beans (Othman et al 2007) Most methods are inhibition methods related to reactive species, which are often free radicals
Meat and meat products are heterogeneous foods contained the intrinsic antioxidants, including tocopherols, carnosine, and antioxidants enzymes with their total antioxidant capacity (TAC) Determining TAC of complex beef samples is not a simple manner This TAC must be evaluated by various methods because each method relates to various chemical mechanisms and express various aspects of the antioxidant properties Moreover, determining different antioxidant molecules separately is not practical Therefore, an indirect method is to measure the total antioxidant activity (TAA) (Koracevic et al 2001), total antioxidant capacity (TAC) (Miller et al 1993) (Erel 2004), (Koracevic et al 2001), (Miller et al 1993) have developed the different measurement methods, including Ferric Reducing Antioxidant Power (FRAP) method (Benzie and Strain 1996), Trolox Equivalent Antioxidant Capacity (TEAC) method (Re et al 1999), and Thiobarbituric Acid Reactive Substances (TBARS) method These various methods are to determine TAC of samples based on colorimetric method The working reagent is saturated thiobarbituric acid (TBA) solution in the TBARS method while colored FRAP reagent in the FRAP method and FC reagent in Folin-Ciocalteu (FC) method (Stratil et al 2006), (Lee et al
The FRAP method (Benzie and Strain 1996) is a novel method for evaluating
―antioxidant power‖ based on the reduction of ferric ion caused by antioxidant compounds A colored ferrous-tripyridyltriazine complex is formed through the by reading the absorbance at 593 nm in test samples, then compared with those on the standard curve built from pre-determined concentration of ferric ion
The TEAC method is based on free radical scavenging by using 2,2’ –azinobis(3- ethylbenzothiazoline-6-sulfonic acid) ABTS + radical cation This is the product of the oxidation of ABTS with potassium persulfate This method determines the antioxidative activity through determining the decolorization of the ABTS + by measuring the reduction of the radical cation as the percentage inhibition of absorbance at 734 nm (Re et al 1999), (Buenger et al 2006), (van den Berg et al
1999) Absorbance values are also projected onto the regression line built from the standard trolox (Re et al 1999)
The FC method is based on the degradation of a phosphowolframate- phosphomolybdate complex into blue reaction products under phenolics presence (Stratil et al 2006), (Vinson et al 1998) FC reagent is used to determine the amount of phenolic compounds
The TBARS method is based on the reaction of TBA with secondary products from lipid oxidation of unsaturated fatty acids The red chromophore is formed and measured by spectrophotometer (Sứrensen and Jứrgensen 1996)
In Vietnam, fresh meat is exposed under environmental conditions such as sunlight, temperature, moisture, and oxygen Consequently, the increase in oxidant agents from natural environment and the decrease in intrinsic antioxidants as tocopherols, carnosine, and antioxidant enzymes cannot be prevented These intrinsic antioxidants of meat are one of the important major for preventing lipid oxidation Therefore, the aim of this study was to determinate the effect of market type and display time on lipid oxidation of raw beef across three regions of Vietnam through measuring total antioxidant capacity and TBARS value in beef by the mentioned methods In addition, the efficiency comparison of these 4 methods was carried out
For this study, raw beef samples were collected from the three representative regions of Vietnam, Ho Chi Minh City (HCMC), Da Nang (DN), and Ha Noi (HN) on the three types of markets (supermarket (SM), indoor market (IM), and open market (OM)) at two sampling times (the opening time (T0) and the closing time (T4)) Five 300-g Longissimus muscle samples were collected, packed in zip plastic bags and kept in the Igloo Super Tough Sportsman ice chest (Igloo, Katy, TX) with ice packs The samples were transferred immediately from the market into the freezer (-20 0 C) at laboratory Then, they were divided into about 0.5 g sample for each PP tube and kept at -20 0 C for chemical analyses
2,4,6-Tris(2-pyridyl)-s-triazine (TPTZ) (T1253), 2,2’ –Azino-bis(3- ethylbenzothiazoline-6-sulfonic acid) diammonnium salt (ABTS) (A1888), trolox ((±)-6-hydroxy-2,5,7,8-tetramethyl-chromane-2-carboxylic acid) (238813), 1,1,3,3- Tetramethoxypropane (TMP) (108383) were purchased from Sigma-Aldrich (St
Louis, MO, USA) Butylatedhydroxytoluene (BHT) (822021), Iron (III) chloride (803945), Sodium carbonate (106392), 2-thiobarbituric acid (TBA) (108180), Folin- Ciocalteu (FC) (109001), Methanol (HPLC grade) were purchased from Merck (Darmstadt, Germany Distilled water (D-water) was used in the four methods
Trolox was used as an agent to construct the standard curve for FC, FRAP, TEAC
Trolox was dissolved in methanol (8 mM) The stock solution was diluted to four lower concentrations as follows 0.8, 0.6, 0.4, 0.2, and 0.1 mM
The standard solution of TBARS is prepared from the diluting and extracting solution (DESol); stocking solution (10 mM) TMP in 10% TCA and 50 ppm BHT Stock solution was diluted to 100 àM, and then diluted from 100àM to 0, 2.5, 5.0, 7.5 àM
0.5-g samples were placed into 15-ml PP tubes which added 2 mL of methanol, and shook vigorously in 5 min Then, they were centrifuged at 3000 x g in 10 min at room temperature After transfering 1.5 mL supernatant into another 2-mL PP micro- centrifuge tube, they were centrifuged at 10.000 x g for 15 min at 4 0 C This extracted antioxidant was used for FC, FRAP, and TEAC
For TBARS method, sample extractions were collected through DESol as follows:
0.5-g samples were put into 15-mL PP tubes which had already added 2 mL DESol; the tubes were then incubated in water (at 90 o C) in 30 min They were chilled in ice and centrifuged at 3000 x g for 10 min at 4 0 C
75 àL FC reagent was mixed with 150 àL sample (test samples) or 150 àL trolox (standard) or 150 àL methanol (blank sample) This mixture was vortexed in 10 s, left still in 3 min at room temperature, then added into 1125 àL D-water with saturated 150 àL Na 2 CO 3 This mixture was vortexed in 10 s and centrifuged at 10.000 x g in 5 min at 25 0 C The absorbance was read at 765 nm
Ferric Reducing Antioxidant Power (FRAP) Method
The FRAP method was described by (Benzie and Strain 1996) The reagent includes 100 mM acetate buffer, pH 3.6; 10 mM TPTZ in 40 mMHCl; 20 mM FeCl 3 in D- water FRAP reagent was prepared by mixing 125 mL acetate buffer, 12.5 mL TPTZ solution, and 12.5 mL FeCl 3 in D-water solution 300 àL of working FRAP reagent was mixed with 1155 àL D-water and 45 àL test samples or blank samples This was vigorously vortexed, left at room temperature in 10 min, and then centrifuged at 10.000 x g in 10 min at 25 0 C The absorbance of the sample was read at 593 nm
Trolox Equivalent Antioxidant Capacity (TEAC) Method
EFFECTS OF MARKET SETTING AND TIME OF PURCHASE ON
EFFECTS OF MARKET SETTING AND TIME OF PURCHASE ON COUNTS OF AEROBIC BACTERIA, ESCHERICHIA COLI , AND COLIFORM OF OF
BEEF ( Longissimus Muscle) IN VIETNAM
P T T Vu 1 , A K McCain 2 , N T Mai 1 , M V V Le 1 , D H Nguyen 1 , and T T N Dinh 2
1 Department of Food Technology, Ho Chi Minh City University of Technology, Ho Chi
2 Department of Animal and Dairy Sciences, Mississippi State University, Mississippi State,
The objective of this study was to determine the effect of market type, and display time on microbiological quality of 180 beef samples collected in Ha Noi, Da Nang, and Ho Chi Minh City at the opening of the market (T0) and 4 h after the opening (T4) in Vietnam Beef samples had more than 11.6, 7.0, and 9.1 logs of aerobic plant count (APC), E coli, and coliforms, respectively In supermarket (SM), E coli was greater at T0, whereas it was greater at T4 in indoor market (IM) (P market type × sampling time
= 0.029) These results emphasized the high level of bacterial counts in beef at retails in Vietnam These high levels of the bacterial counts reflected in the beef quality and were one of main factors causing off-odors, and off-flavors in beef Moreover, these high levels of bacterial counts due to the influence of market type and display time (P
Beef, Escherichia coli, Coliforms, Aerobic Plant Count, Microbiological Quality
Meat is one of the most perishable foods because of its high water content and abundance of important nutrients available on the surface (Gram et al 2002), (Labadie 1999) Hence, the numbers and kinds of microorganisms found on fresh meat are highly variable The microorganisms firstly affected by the conditions on meat surfaces APC and E.coli are likely the main hazards to meat at normal pH at room temperatures because of their largely uninhibited growth at this temperature under aerobic conditions (Gill and Newton 1980) E.coli biotype I is one of the predominant Enterobacteriaceae in ground beef (Ng and Stiles 1978), (Cox and Mercuri 1978) In addition, many studies have explored the use of indicator organisms such as E.coli to predict potential spoilage of meat (Milios, Drosinos and Zoiopoulos 2014), (Brown, Longworth and Waldron 2002), (Stiles and Ng 1981) APC has been recommended as a useful tool in microbiologically assessment evaluating food quality High mesophilic counts (25 – 37 0 C) may indicate unsatisfactory hygiene or the use of heavily contaminated raw materials (Lillard et al 1984), (Thatcher and Clark 1968), (Al‐
Fresh meat quality depended on the complex multi-factors, including the microbial quality, a wide range of physical or chemical reactions (in't Veld 1996) The microbial quality of meat was determined based on hygienic condition of premises, surfaces equipment, slaughtering utensils (Gilbert and Watson 1971), (Nortje et al 1989), (Patterson and Gibbs 1978), (Field et al 1977), and environmental factors, including sunlight, pH, moisture, temperature (in't Veld 1996), oxygen, and water activity (Jaye, Kittaka and Orda 1962) Temperature is one of the most important factors influencing bacterial growth in meat and meat products One of the recent researches has that discovered microorganism growth are not limited to specific ranges of temperature (Mager et al 1993), pH (Hill, O'Driscoll and Booth 1995) For instance, in the presence of high numbers of spoilage psychrotrophs, E.coli was not inhibited at 20 or
30 0 C under aerobic conditions, or at 30 0 C under anaerobic conditions (Gill and Newton 1980)
Meat quality was affected by vacuum and modified atmospheres (MA) packs because of the important effect on the microorganisms (Labadie 1999) Vacuum packs limited quantity of oxygen which inhibited the growth of aerobic bacteria and increased anaerobic bacteria quantity In case stored under aerobic conditions, a few aerobic bacteria dominated the meat system and actively contributed to the slight changing quality of meat (Koutsoumanis et al 2006)
In Vietnam, fresh meat is exposed under environmental conditions such as sunlight, temperature, moisture, and oxygen These are the main causes for changing quantity of microorganisms Therefore, the objective of this study was to evaluate the effect of environmental factors, including market type and display time on the specific growth rate of APC, E.coli, and coliform
Beef samples in the ice chests were transported back to a local university in each region Samples were weighed (approx 200g) and put into the Whirl-Pak ® bags (Nasco, Fort Atkinson, WI) Then, samples were added 90 mL of Buffered Peptone Water broth (BPW; 25.5 g/L; 3M, St Paul, MN); (Vipham et al 2012) and shaken in 60s Two sterile 15-mL polypropylene tubes (Greiner Bio-One, Monroe, NC) of BPW rinsate were collected and stored on ice for transportation to Ho Chi Minh City University of Technology for further analyses
Except for sterile sampling bags, all apparatuses and solutions were autoclaved before microbiological analyses Blank enrichment, isolation, and incubation of all solutions including sterile water were performed for all microbiological analyses
Aerobic Plate Count (APC), E coli, and coliforms analyses were carried out according to the Official Method of Analysis 990.12 (APC; AOAC International, 2012) and 998.08 (E coli and coliforms; AOAC International, 2008) with 3M™
Petrifilm™ Aerobic Count Plates and 3M™ Petrifilm™ E coli/coliforms Plates serially diluted (1:100) to a volume of 1.5 mL with sterile BPW broth in two 2-mL sterile polypropylene microcentrifuge tubes for either APC or E coli/coliforms 1 mL of each dilution was spread onto an APC Petrifilm™ or an E coli/Coliform
Petrifilm™ The Petrifilms™ were incubated with clear side up in a stack of 10 at 35°C in 24 h Colony forming units (CFU) were counted according to the 3M interpretation guides (3M, 2015b; 3M, 2015c)
Aerobic Plate Count (APC), E coli, and coliforms were reported as log CFU/g, calculated from CFU as follows: log CFU/g = log (N
V DF V 0 m) with N, V, DF, V 0 , and m being number of colony forming units on a Petrifilm™, volume of a dilution spread onto a Petrifilm™ (1 mL), dilution factor, original volume of BPW rinsate (90 mL), and sample weight (g), respectively
APC, E coli, and coliforms, the experimental until was beef sample (n = 30 per factorial combination) The effects of market type and sampling time on bacterial count (log CFU/g) were statistically analyzed by SAS version 9.4 (SAS Institute, Inc., Cary, NC, USA) The normally distributed data (log CFU/g) was performed through linear regression A generalized linear mixed model was used in the GLIMMIX procedure of SAS, with market type, sampling time, and their interaction being the fixed effects and region being the random effect Means were separated by the protected t-test, using the LSMEANS statement with the PDIFF option in the GLIMMIX procedure Statistical significance was determined at P ≤ 0.10
APC of beef in all markets increased from 11.61 log CFU/g to 11.64 log CFU/g (Figure 4.1 and Figure 4.2)
Figure 4.1: Aerobic Plate Count (APC), E coli, and coliforms bacterial count of beef purchased at the supermarket (SM), indoor market (IM), and open market (OM), across three regions of Vietnam (Ho Chi Minh City, Da Nang, and Ha Noi) Within a category of bacterial count, means without common letters differ, (Pmarket type = 0.060, 0.380, 0.005, respectively)
SM IM OM log CFU/g
Figure 4.2: Aerobic Plate Count (APC), E coli, and coliforms bacterial count of beef purchased at two sampling times (opening - T0 and 4 h after opening - T4) Within a category of bacterial count, means without common letters differ, (P time = 0.034, 0.837, 0.196, respectively)
Coliforms of all beef samples increased from 9.43 log CFU/g to 10.38 log CFU/g
(Figure 4.1 and Figure 4.2) Many of the APC Petrifilm™ and E coli/coliforms
Petrifilm™ were too numerous to count (TNTC) at 10 -6 dilution, because they contained a pink (APC and coliforms) or purple (E coli) color in the entire growth area (3M, 2015b) These TNTC Petrifilms™ were estimated at 10 8 CFU This result showed that market types significantly affected the APC and coliforms values of all beef samples (P = 0.060 and 0.005, respectively; Table 4.1) More specifically, there are significant differences between the OM and SM in APC value (11.61 log CFU/g, 11.62 log CFU/g, respectively; Table 4.1, P = 0.02; Figure 4.1) Furthermore, the significant difference in coliforms of beef samples was found in IM compared to SM and the OM compared to SM (P = 0.007 and 0.003, respectively; Table 4.1) The APC and coliforms, excluding E.coli, increased most during display time from T0 to T4
However, only APC value was significantly different between the two display times (P = 0.034; Table 4.2)
Table 4.1: Effect of market type on bacterial counts in beef procured from supermarkets (SM), indoor markets (IM), open markets (OM) across three regions of Vietnam (Ho Chi Minh City, Da Nang, and Ha Noi)
SM IM OM SEM SM SEM IM SEM OM
Aerobic plate count, log CFU/g 11.62 X 11.64 XY 11.61 Y 0.009 0.008 0.007 0.0600 0.1403 0.3726 0.0193
1 Aerobic Plate Count, enumerated using 3M™ Petrilm™ Aerobic Plate Count (3M, St Paul, MN)
2 Escherichia coli, enumerated using 3M™ Petrilm™ E coli/Coliform Count Plates (3M, St Paul, MN)
3 Coliform, enumerated using 3M™ Petrilm™ E coli/Coliform Count Plates (3M, St Paul, MN)
XY LS means with like letter do not differ (P < 0.1) SEM: standard error of the mean
SUMMARY AND CONCLUSIONS
Evaluating effect of market type and display time on quality of raw beef is necessary for beef consumption in the current Vietnam situation Consumers in Vietnam are accustomed to buying unpackaged raw meat which is exposed under open atmosphere, temperature, and sunlight at traditional markets These environmental conditions mainly impact on the quality of meat including chill storage conditions at supermarket The objectives of the present study were: 1) to investigate the effect of three market types and two sampling times on the formation and the development of off-odors as well as off-flavors in beef in Vietnam; 2) to explore the effect of two above factors on the lipid oxidation through two indicators identified as total antioxidant capacities (TAC) and secondary products of oxidation (TBARS); and 3) to evaluate the counts of aerobic bacteria quantity grown on meat surface affected by different market types and sampling times
Off-odor/ off-flavor descriptors about beef meat were formed by the descriptive panel LiveryR represented the effect of market type on sensory quality of meat while sourR, sweetR, liveryC indicated the impact of display time Over all, off- odors and off-flavors could be used for representing of the lipid oxidation in fresh beef meat This study complements the previous studies in terms of the origin and the growth of off-odor/off-flavor of fresh beef meat displayed at retail market in developing countries like Vietnam
On the other hand, determining oxidative extent of raw beef based on TAC and TBARS indicators expressed that market type and display time had impact on the oxidative extent of raw beef While TAC value was indicative of the effect of market type and display time on lipid oxidation, TBARS value only revealed for the effect of market type Therefore, TAC indicators could be a good instrumental measure for the determination oxidation of raw beef meat during storage
Besides, the development of aerobic bacteria counts also reflected the quality of meat Aerobic plant count was affected by both market type and display time
Coliforms counts were affected by the display time
In general off-odor/off-flavor descriptors, TAC and TBARS values, and APC,
E.coli and coliforms counts has proved the effect of market type and display time on quality of raw beef meat However, the differences were minimal and may not be meaningful The result is an overview of the fresh beef quality displayed on Vietnam market and is necessary data to provide knowledge for consumers in the retail market This result indicated risk for beef consumers in Vietnam because Indicator organism counts were higher than standard of Vietnam (TCVN 7046 : 2002) The high incidence and bacterial loads could be partially attributed to the improper practices at the markets and various sources at the production level
Therefore, more research is needed in this area to risk mitigation can be devised
For sensory quality, developing consumer panel is necessary to compare the result of descriptive panel
APPENDICES APPENDIX A DATA FOR CHAPTER 2
Instruction of descriptor development for beef sample
Thank you for your participation in this study Your assistance is appreciated
The objective of this session is to evaluate the flavor and taste of beef products
Please take your time, proceed at your own rate, and evaluate the samples carefully
After filling out the sample information, please begin sampling
For fresh samples: Sample is placed in plastic cup Panelists hold cup to put up near the nose and breathe in three times shortly
For cooked sample: Sample is covered aluminum foil, with random 3-digit numbers The first, panelist open paper, put up near nose and breathe in three times shortly Second, the sample is cut through with the molars after 5 - 10 chews
Before each sample, please take a bite of cracker and drink water
Please answer the questions on a CATA question ballot Then, relax 3 -5 min before evaluate next sample If you have any questions, please ask the monitor for assistance
Note: Don’t place too close nose, avoid phenomenon ―shock‖ olfactory, influent the next evaluation
Upon completion of the ballot please give it to the monitor
Thank you again for your help and invaluable opinions
A CATA QUESTION BALLOT PANELIST ID: _ _PANEL DATE: _
Fill out the following information by circling the numbers correspond to all the words which they consider appropriate to describe a product
Instruction of estimation intensity test
Thank you for your participation in this study Your assistance is appreciated
The objective of this session is to evaluate the flavor and taste of beef products
Please take your time, proceed at your own rate, and evaluate the samples carefully
After filling out the sample information, please begin sampling
For fresh sample: Sample is placed in plastic cup, with random 3-digit numbers
Panelists hold cup to put up near the nose and breathe in three times shortly
For cooked sample: Sample is covered aluminum foil, served warm at 60 0 C on plastic dish, with random 3-digit numbers The first, panelist open paper, put up near nose and breathe in three times shortly Second, the sample is cut through with the molars after 5 - 10 chews Before each sample, please take a bite of cracker and drink water
Panelists will receive different intensity level sample at the each time Panelists will estimate the intensity of flavor on a scale Relax 3 -5 min before evaluate next sample If you have any questions, please ask the monitor for assistance
Note: Don’t place too close nose, avoid phenomenon ―shock‖ olfactory, influent the next evaluation
Upon completion of the ballot please give it to the monitor
Thank you again for your help and invaluable opinions
Ballot of estimation intensity test
ANSWER BALLOT PANELIST ID: PANEL DATE: _
Estimate the intensity of flavor on a scale by choosing one point on scale:
The standard curve of FC method
The standard curve of FRAP method y = 0,7704x + 0,0385 R² = 0,9907
Absorbance Trolox FC trolox (FC) Linear (trolox (FC)) y = 1,5976x + 0,132 R² = 0,9752
Absorbance Trolox FRAP trolox (FRAP) Linear (trolox (FRAP))