The combination of microbiological, biochemical, and quality index methods in quality evaluation of pacific white shrimps (Litopenaeus vannamei) preserved at 0°C

Nội dung text: The combination of microbiological, biochemical, and quality index methods in quality evaluation of pacific white shrimps (Litopenaeus vannamei) preserved at 0°C

1. Doi: 10.31276/VJSTE.63(2).45-51 Life Sciences | Agriculture The combination of microbiological, biochemical, and quality index methods in quality evaluation of pacific white shrimps (Litopenaeus vannamei) preserved at 0°C Nhat Tam Le 1*, Nguyen Que Anh Huynh1, Nhu Khue Doan1, Thuy Xuan Uyen Phan1, Ba Thanh Nguyen1, Sao Mai Dam1, Thi Van Thi Tran2, Le Phuong Lien Nguyen3, Van Hai Chu4, Huynh Anh Vu Truong4 1Institute of Biotechnology and food technology, Industrial University of Ho Chi Minh city, Vietnam 2Hue University of Science, Hue University, Vietnam 3Department of Refrigeration and Livestock Product Technology, Szent István University, Budapest, Hungary 4Center of Analytical Services and Experimentation Ho Chi Minh city, Vietnam Received 28 May 2020; accepted 21 August 2020 Abstract: In this study, the sensory, microbiological, and biochemical qualities were used to examine the quality of Pacific white shrimps (Litopenaeus vannamei) preserved at 0°C during a 10-day period. The sensory quality was evaluated by a quality index (QI) that resulted from a quality index method (QIM) scheme. Meanwhile, the total viable count (TVC) and K-value were used to assess the microbiological and biochemical qualities of the shrimp. On day 9, the results from TVC and QIM have shown that the shrimp showed signs of spoilage, corresponding to a log CFU/g of 6.4 and a QI of 21.37, which is unacceptable to consumers. The QI increased linearly with storage days therefore the remaining shelf-life of the shrimp was estimated from a linear regression equation. In particular, this study found a linear relationship between QI, K-value, and hypoxanthine content. Furthermore, hypoxanthine itself could be considered as an independent quality index like the K-index. In conclusion, the quality of Pacific white shrimp was categorized into four different classes: excellent, good, acceptable, and moderately acceptable, based on its sensory and biochemical quality indicators. Keywords: hypoxanthine, K-value, pacific white shrimp, QIM. Classification number: 3.1 Introduction qualities are established based on these impact factors [2]. The organoleptic quality assessment method is based on Shrimp are an important source of seafood with variations of sensory properties including the color, smell, considerable nutrition and economic value in many taste, and texture. The intensity rating method is considered countries around the world [1]. In Vietnam, Pacific white shrimp (Litopenaeus vannamei) have achieved a high the most popular at present, followed by the Torry scheme, export turnover rate in the seafood industry in recent years. quantitative descriptive analysis (QDA), and QIM, to name However, the method used to assess the quality of shrimp a few. Among those, QIM is predicted by Hyldig as the in particular, and seafood in general, is not consistent with potential method for quality assessment in the European the current methods in other parts of the world. The quality Community. QIM was developed by the Tasmanian Food of post-harvest shrimp decreases with storage time due to Research Unit in Australia [4] and is continually being the impact of three main factors, which include the activity developed. QIM possesses many advantages such as short of endogenous enzymes, microorganisms, and chemical training time, short evaluation time, and high reliability in reactions. These activities alter the sensory state, chemical assessing the freshness of seafood preserved in ice [5]. The composition, as well as the total amount of aerobic difference between QIM and other methods is that QIM is microorganisms in shrimp [2, 3]. Therefore, methods that built to evaluate the sensory changes of specific species. assess sensory, chemical, microbiological, and physical QIM focuses on the correlation between the quality index *Corresponding author: Email: lenhattam@iuh.edu.vn Vietnam Journal of Science, June 2021 • Volume 63 Number 2 Technology and Engineering 45
2. Life Sciences | Agriculture and the storage time expressed via a linear regression Reagents equation. Thus, QIM allows an estimation of the remaining Reagents including Adenosine-5’-triphosphate shelf-life of seafood. So far, QIM-Eurofish has developed (PubChem CID: 5957), Adenosine-5’-diphosphate 28 QIM schemes mainly for fish, shrimp, and squid species. (PubChem CID: 6022), Adenosine-5’-monophosphate However, the QIM scheme for Pacific white shrimp has (PubChem CID: 6083), Inosinmonophosphate (PubChem not yet been developed [6]. In Vietnam, shrimp quality is CID: 8582), Inosine (PubChem CID: 6021), and assessed according to TCVN 3276-89 [7]. This standard is hypoxanthine (PubChem CID: 790) were purchased from generally applied to all shrimp species and is not an intensity Sigma - Aldrich (Merck KGaA, Germany). Other reagents rating method, however, it is a semi-quantitative assessment such as methanol (PubChem CID: 887), ethanol (PubChem that describes changes in the properties of shrimp. Therefore, CID: 702), and HPLC-grade water were bought from Merck quality results from TCVN 3276-89 do not resemble those Vietnam Ltd. Co. obtained by the rating method used in importing countries. Determination of TVC This leads to disputes over quality and financial losses for exporting enterprises. After shrimp die, the process of self- TVC was measured according to Leboffe and Pierce decomposition takes place immediately, which is followed (2015) [16]. In brief, 10 g of peeled shrimp were minced by the process of decomposition [8]. This autolysis is and mixed with 90 ml of 0.9% NaCl solution and then caused by endogenous enzymes in the shrimp and results centrifuged at 3000 rpm at 30oC for 5 min. The pour-plate in the release of nucleotides and its derivatives. In 1959, method using plate count agar was applied to determine Saito and his colleagues introduced the “K-value”, which is the total plate counts. The extract from the samples were calculated based on nucleotides and their derivatives. The inoculated on agar plates and incubated at 30oC for 48 h “K-value” has been formulated as an index of freshness before the colonies were counted. The experiments were in seafood [9]. Unlike quality indicators such as TVB-N, repeated three times and the TVC values were expressed as TMA-N, or histamine that are suitable for assessing quality log CFU/g (colony forming units). during the decomposition stage, the K-value tends to Development of QIM scheme linearly correlate with storage time [10-15]. This allows The QIM scheme was developed based on three main researchers to develop a regression equation between the steps according to Bernardi, et al. (2013) and Le, et al. QI and K-value. (2017) [17, 18], which include: (1) identification of quality Therefore, this study aims to develop a complete attributes, (2) main sensory evaluation, and (3) quantification quality assessment process including the analytical of the developed (sensory) QI, as mentioned below. methods measuring the microbiological, biochemical, and Step 1 (preliminary program): three sensory experts sensory changes. The expected findings include the quality observed all the changes in quality attributes (e.g. shape, classification of Pacific white shrimp based on the QI and odor, texture, eyes, shell color, and formation of black spots K-value as well as the linear regression equations between on the abdomen, body, tail). The terms were noted from the quality indicators investigated. direct observation [18-20]. The CATA (check all that apply) Materials and methods method was applied to select the most suitable descriptive terms from the preliminary terminology. Each attribute was Shrimp collection and storage then given a score from 0 to 3, with a low score suggesting Healthy Pacific white shrimp were purchased from the a high quality level. Binh Dien market in Ho Chi Minh city. The shrimp samples Step 2 (main program development and panel training): were then washed with filtered water and packaged in the shrimp samples were evaluated daily for ten consecutive polyethylene zipper bags (26.8×27.9 cm) (Alcoa Products days at 0°C. The start of day 0 was determined to be right after Inc., VA, USA). These sample bags were placed directly in the shrimp arrived at the testing facility. The examination a polystyrene container containing shaved ice with a ratio of the shrimp at different time points was conducted by six of 1 shrimp to 2 shaved ices (w/w) and were delivered to sensory panelists for one month. The panelists evaluated the testing facility within 2 hours. At the testing facility, the samples and recorded the results without knowing the the sample bags were preserved at 0°C in a refrigerator for storage time. This process ensured accuracy, reliability, and research purposes. minimized bias in data. Vietnam Journal of Science, 46 Technology and Engineering June 2021 • Volume 63 Number 2
3. Life Sciences | Agriculture Step 3 (quantification of the recorded sensory QI): this Results and discussion step primarily involved quantification of the data collected The change in TVC from the QIM scheme. The regression equation between the days in storage and QI was developed to compare the The initial number of microorganisms in shrimp was projected shelf life with actual shelf life of shrimps. The mainly from the breeding environment [23]. The shrimp data collected from ten different samples corresponded to samples, after being washed with clean water, were stored each of the 10-day storage periods. at 0°C and the TVC with a log CFU/g value of 4.7 was recorded on day 1. The TVC values ​​for the following days ATP, related compounds, and K-value 2, 3, and 4 did not change significantly with 4.78, 4.89, Nucleotides and related compounds including ATP, and 5.01 (log CFU/g), respectively. However, starting ADP, AMP, IMP, inosine, and hypoxanthine were from day 5, significant changes were observed (p<0.05). measured by high-performance liquid chromatography The TVC value was 5.55 on day 5, 5.78 on day 6, 5.77 with a diode array detector (HPLC-DAD). In this method, on day 7, 5.89 on day 8, 6.4 on day 9, and 6.4 on day 10. nucleotides and related compounds were extracted with The TVC values ​​increased rapidly after day 4 for 10 days 0.6 M perchloride acid and detected by the 2018 Cosmosil and exceeded 6 log CFU/g on day 9. The value of 6 log application (Nacalai Tesque, Japan) and Veciana-Nogues, et CFU/g is regarded as the limit allowed by the International al. (1997) [21, 22]. In summary, 3±0.01 g of shrimp meat Commission on Microbiological Specifications for Foods was blended with 10 ml of 0.6 M perchloride acid for 10 (ICMSF) for frozen shrimp. Thus, the shelf life of shrimps min by vortex. The mixture was then centrifuged at 3000 was set at day 8. Two recent studies by Naik, et al. (2014) [23] and Okpala, et al. (2014) [24] on black tiger and white rpm for 10 min to collect the supernatant. This process was shrimp samples have also shown that the shelf life are 8 repeated three times. The extract was neutralized to pH 7.0 days and 7 days, respectively. This difference in shelf life using 1 M KOH filtered through Whatman Grade 1 filter may be from different species, seasons, harvest techniques, paper (Sigma-Aldrich, Germany) and diluted to 50 ml by age, and physiological conditions [2]. Microbiological volume. One milliliter of the diluted extract was uploaded changes in shrimp are closely related to sensory and into an SPE C18 column (Agilent Technologies, USA) and biochemical changes. In the autolytic stage, as mentioned eluted with a 0.05 M K HPO buffer to harvest 10 ml. Then, 2 4 above, the main cause is due to the endogenous enzymes. 50 µl of the harvested extract was injected into the column Some components that are quickly metabolized during this for the analysis of nucleotides and related compounds by period are ATP, glycogen that produces sweet IMP, and HPLC. HPLC analyses were performed using an Agilent hypoxanthine derivatives that produce a bitter taste [2]. A 1260 apparatus (Agilent Technologies, USA) equipped with decrease in pH, which is caused by lactic acid produced from diode array detector (Agilent 1260 detector), 5C18-PAQ glycogen digestion, facilitates the hydrolysis of the proteins column (size 5 mm, length 250 mm - 4.6 mm I.D) (Nacalai of acidic enzymes. The hydrolysis of proteins forms basic o Tesque, Japan) at 30 C. The mobile phase of 0.05 M K2HPO3 substances such as TVB and biological amines [25]. This was controlled at a flow rate of 1 ml/min. Nucleotides and leads to the decomposition of proteins and lipids. This is the related compounds were detected at a wavelength of 260 source of the unique flavors such as alcohols and aldehydes, nm. especially aldehydes that have double bonds in the third The K-value was calculated as the percent ratio of position [26, 27]. Biochemical changes also strongly occur inosine (HxR) and hypoxanthine (Hx) to the sum of ATP during the decomposition stage. TMA compounds have a and degradation products as shown below. fishy smell, which are formed by the reduction of TMAO and NH3 resulting from the metabolism of amine acids by K-values(%)=100(inosine+hypoxanthine)/(ATP+ADP+ enzyme deaminases. AMP+IMP+inosine+hypoxanthine). Development of QIM scheme for the quality evaluation Data analysis of Pacific white shrimps All experiments were conducted in triplicate. The Changes in sensory qualities such as color, odor, obtained data were preprocessed with Microsoft Excel and texture of head and tail were noted with preliminary (version 2010) and analyzed using Statgraphics centurion descriptive terms. The CATA method was applied to software. A linear regression model was fit to the data. The select and arrange the terms in descending quality order as significance level was at p<0.05. described in Table 1 [28]. Vietnam Journal of Science, June 2021 • Volume 63 Number 2 Technology and Engineering 47
4. Life Sciences | Agriculture Table 1. QIM scheme for Pacific white shrimp (Litopenaeus Other shrimp samples with different storage times vannamei). were evaluated by the trained panel for ten consecutive days. Changes in sensory attributes, corresponding QI, and quality class from day 0 to day 10 are presented in Table 2. Characters Description Score Fresh ocean smell 0 Table 2. Sensory changes, QI, and pacific white shrimp quality classifications during storage at 0°C. Lightly fishy smell, smell of seashells 1 Odor Meat Days Descriptions QI Class Neutral or slightly trimethylamine (TMA) 2 Shrimp has fresh ocean smell, blueish-gray head. Strong trimethylamine (TMA) 3 Roes begin to turn yellow. The head has no black spots. Head is intact and tightly attached to the Gray, gray - green, no spot 0 body Body is shiny gray and intact. The back is yellow. 1 1.32 Head Gray, gray - green, light yellow 1 Body has no black spots Tail is gray, a bit purple at the top end and has no Light black, scattered black spots 2 black spots. Tail is attached to the body Shell is hard and tough Black, large black spots 3 Meat is translucent, firm and elastic Excellent Shiny, gray, yellow, spotless 0 Shrimp has fresh ocean smell. Head is blueish- gray. Roes are light yellow. Head has no black Gray, green, some spots 1 Body spots. Head is intact and tightly attached to the body Gray, slightly pink, scattered spots 2 Body is shiny gray and intact. The back is yellow. 2 2.90 Yellow, pink. Large black spots on the Body has no black spots Color 3 body and legs Tail is gray, a bit purple at the tip of the tail, and has no black spots. Tail is attached to the body Gray, purple, spotless 0 Shell is less tough Meat is translucent, firm and elastic Gray, green, some spots 1 Tail Seashell smell, lightly fishy. Roes are yellow Green, pink, large black spots 2 Head is blueish-gray, lightly loose from the body, and has some black spots Black 3 Body is shiny, gray, and green, has no spots 3 Body is intact 5.60 Pearl color, translucent 0 Tail is gray and blue and has some black spots Tail is attached to the body Meat Translucent, silver-ish or gray-ish 1 Shell is less tough and less hard Meat is translucent and grayish. Meat is less firm Milky white 2 Good Seashell and fishy smell. Roes are yellow Milky white, pink, yellow 3 Head is blueish-gray. Black spots appear on the swimming legs. Head is intact Hard, elastic 0 Body is shiny, gray, and green. The body has 4 black spots. Body is intact 8.87 Shell Hard, slight elastic 1 Tail is gray and blue, has some black spots. Tail is attached to the body Slightly soft 2 Meat is translucent, silver gray. Meat is less firm Shell is less tough Soft 3 Seashell and fishy smell. Roes are yellow. Head Head and body are intact. The head is is gray. Black spots appear on the swimming tightly attached to the body. The tail is 0 legs. Head is loose from the body attached to the body Body is gray, and green. The body has black 5 spots. Body is intact but lightly stretched 10.53 Head is loose but body is still intact, and 1 Tail is gray and blue, has black spots. Tail is Texture the tail is attached to the body Appearance attached to the body Head is loosely attached to body; and Meat is milky white and lightly soft 2 Shell is less tough flesh is loosely attached to shell Moderately acceptable Head is very loose, may not attached to Fishy smell. Roes are light orange. Head is the body; flesh is easily separated from 3 pinkish gray. Black spots on swimming legs shell Head is loose from the body Firm, springy, elastic 0 Body is gray; light pink on the back. The body has black spots. Body is intact but lightly 6 14.12 Slightly less firm, less springy 1 stretched Meat Tail is blue and has dark spots. Tail is attached Soft, sticky, slightly elastic 2 to the body Crispy shell Soft, deformed 3 Meat is silver gray and lightly soft Vietnam Journal of Science, 48 Technology and Engineering June 2021 • Volume 63 Number 2
5. Life Sciences | Agriculture Fishy, ammonia smell to the loose body. The shrimp had a reddish body with a Roes are light orange. Head is pinkish gray moderate density of black spots and opaque shell. The meat Black spots on swimming legs and head. Head is loose from the body was not attached to the skin. It was slightly pink, soft, and Body is gray and pink. The body has large black 7 16.93 had slightly sour smell, which acquired QI scores of 16.93 spots. Body is stretchy Tail is blue, pink and has dark spots. Tail is and 18.50, respectively. In stage 5 (from day 9 to day 10), attached to the body the head was almost detached from the body, the shrimp had Crispy shell Meat is milky gray and soft. Just a foul and sour smell, soft meat, a lot of black spots, and no Fishy, slightly trimethylamine odor acceptable legs. The QI scores during this stage were 21.37 and 22.77, Roes are orange and broken. Head is pinkish respectively. A linear relationship between storage days and gray. The head has large black spots. Head is loose from the body QI score was found by a simple linear regression equation: Body is gray and pink. The body has large black 8 18.50 QI=2.4×day-0.79 (R²=0.990). The shelf life of Pacific white spots. Body is stretchy Tail is blue, pink at the tip of the tail. Tail is shrimp at 0°C was projected to 8 days corresponding to QI attached to the body of 18.5. Le, et al. (2017), Okpala, et al. (2014), Nirmal, et al. Crispy shell Meat is milky gray and soft, not elastic, sticky (2009), and Hanpongkittikun, et al. (1995) [18, 24, 29, 30] Fishy, trimethylamine odor also obtained a shelf-life for black tiger and white shrimp Head is orange, and black. Large black spots ranging between 7 and 8 days. In reference to previously Head is loose from the body. Roes are broken Body is yellow, pink. Body has large black spots published studies, we categorize the quality of Pacific white 9 Black spots appear on the abdomen. Body is 21.37 shrimp into 4 classes: Excellent (QI from 0-2.9), Good (QI stretchy Tail is black. Tail is attached to the body 2.9-8.87), Moderately Acceptable (QI 8.87-14.12), and Just Soft shell Acceptable (QI 14.12-18.50). The established QIM scheme Meat is milky white, yellow, pink. Meat is sticky Rejected was validated by comparison between its projected shelf- Strong trimethylamine smell (rotten smell) Head is orange, black. Large black spots. Head is life and the actual shelf-life of the shrimp samples. Ten loose from the body. Roes are broken shrimp samples with different storage times were randomly Body is yellow, pink. Body has large black spots. 10 Black spots are on the abdomen and legs. Body 22.77 selected and subjected to the QI evaluation. The QI score is stretchy for each sample was the average score given by the sensory Black tail. Tail is attached to the body Soft shell panel. The estimated shelf life was calculated using the Meat is milky white, yellow, pink. Meat is sticky linear regression equation (QI=2.41×day-0.79; R²=0.990). The results in Table 3 show that the actual shelf life was not The changes in the sensory quality of Pacific white significantly different from the estimated shelf life (p<0.05). shrimp were divided into five stages corresponding to five Table 3 describes the data from the 10 experimental samples. storage periods: from day 1 to day 2; from day 3 to day 4; Table 3. Validation of the QIM scheme with the projected and from day 5 to day 6; from day 7 to day 8; and from day the actual shelf life. 9 to day 10. In stage 1 (from day 1 to day 2), the shrimp underwent a period of stiffness and there were almost no Equivalent number Projected shelf life Actual changes in color, texture, and odor. The QI scores of day Samples QI of storage days according to QIM shelf life in ice scheme (n=3) 1 to 2 went from 1.32 to 2.9, respectively. In stage 2 (from day 3 to day 4), the sensory characteristics of the shrimp 1 1.14 0.8 7.2 7.07±0.06 were similar to those on days 1 and 2, however, the color of 2 2.82 1.5 6.5 6.5±0.10 head and tail began to change and therefore the QI scores 3 4.27 2.1 5.9 5.97±0.12 were 5.60 and 8.87, respectively. In stage 3, (from day 5 4 6.43 3.0 5.0 5.03±0.12 to day 6), the shrimp shell lost its glossiness and became 5 10.04 4.5 3.5 3.57±0.15 slightly opaque. At this point, the shrimp were still quite fresh, milky white, and slightly soft, but they had lost their 6 13.17 5.8 2.2 2.23±0.15 elasticity and had a few black spots on the head and tail. 7 2.58 1.4 6.6 6.50±0.10 Thus, the QI scores were between 10.53 and 14.12. In 8 12.93 5.7 2.3 2.23±0.12 stage 4 (from day 7 to day 8), the color of the head and tail 9 6.92 3.2 4.8 4.97±0.15 changed considerably compared to the initial samples. The 10 9.80 4.4 3.6 3.50±0.10 head and tail were slightly black and the head was attached Vietnam Journal of Science, June 2021 • Volume 63 Number 2 Technology and Engineering 49
6. components in the following days: the amount of AMP decreased steadily; IMP increased until day 6 then decreased slightly to day 10; HxR almost did not change; while Hx increased gradually over the storage time. Thus, among the components considered, the Hx value increased linearly with the storage time and the linear regression equation between Hx and the storage day was Hx = 0.177×day + 0.33 (R2 = 0.974). The K-value calculated from the equation increased with time of storage. The linear regression equation between the K- value and storage day was K-value = 3.05×day + 1.8 (R² = 0.992) (Fig. 2). Studies [10-15, 31] also show that the K-value and hypoxanthine amount increase linearly with storage time. This suggests that it is possible to use the amount of hypoxanthine to Life Sciences | Agriculture assess the quality change of Pacific white shrimps preserved at 0°C using the linear regression procedure between the K-value and hypoxanthine presented above. Table 3 shows that the remaining shelf-life of the 8 ATP samples were nearly equal to the shelf-life calculated from 7 ADP the linear regression equation between QI and storage days. 6 AMP IMP This validated the efficiency of the QIM scheme for Pacific 5 HxR white shrimp and proved that this scheme can be used to 4 Hx evaluate the quality and the classification of shrimp quality 3 as shown in Table 2. muscle of µmol/g 2 1 The change in K-value Days 0 Shrimp undergo the autolysis process quickly after 0 1 2 3 4 5 6 7 8 9 10 harvest. ATP is one of the first metabolites in fisheries after Fig. 1. CFig.hanges 1. Changes in nucleotide in nucleotide content content and theand compositionthe composition of derivativesof death. The changes in nucleotide and related compounds are derivatives during 10-day storage. Adenosine triphosphate - during 10-day storage. (Adenosine triphosphate - ATP; Adenosine diphosphate - presented in Fig. 1. From this figure, the changes of ATP, ATP; Adenosine diphosphate - ADT; Adenosine monophosphate ADT; Adenosine- AMP; Inosine monophosphate monophosphate - AMP; - InosineIMP; Xanthine monophosphate - HxR; - IMP; ADP, AMP, IMP, and inosine became quickly prone dueXanthine to Hypoxanthine- HxR; Hypoxanthine - Hx. - Hx). the endogenous enzymes possess in fish and shellfish. In contrast, the transformation from hypoxanthine to uric acid 40 occurred slowly. Therefore, the amount of hypoxanthine 35 K % increased with the storage time. Fig. 1 depicts the ATP content 30 and its derivatives resulting from the ATP autolytic process. 25 The ATP components and their derivatives are expressed 20 y=3.05x+1.77 15 R²=0.992 in µM/g. The contents of ATP, ADP, AMP, IMP, HxR, and 10 Hx measured on day 1 were 0.4, 1.07, 7.03, 0.4, 0.44, and 5 0.59 µM/g, respectively. This proved that the metabolism Days 0 from ATP to AMP occurred quickly at the beginning. The 0 1 2 3 4 5 6 7 8 9 10 11 amount of ATP and ADP from the 3rd day onward had very Fig. 2. Changes of K-value during 10-day storage. low values in the remaining days. The amount of AMP Fig. 2. Changes of K-value during 10-day storage. decreased rapidly until day 4 (4.12 µM/g), meanwhile, the CorreCorrelationlation be twbetweeneen the qtheual itqualityy indic eindicess and claandssi fication of amount of IMP, Hx, and HxR increased graduallys htor i1.24,mp quclassificationality of shrimp quality 1.09 , and 0.84 µM/g, respectively, on day 4. However, there The results showed that the QI, K-value, and hypoxanthine The results showed that the QI, K-value, and hypoxanthine were differences in these components in the followingcorr edays:lated linearly with storage time. Therefore, these quality correlated linearly with storage time. Therefore, these the amount of AMP decreased steadily; IMP increasedindi cuntilato rs correlate linearly with each other. The linear regression quality indicators correlate linearly with each other. The 2 day 6 then decreased slightly to day 10; HxR almostequa t didion between the indicators are as follows: QI = 0.79K - 9.49 (R linear regression equation between2 the indicators are as 2 not change; while Hx increased gradually over the= storage0.956 ); QIfollows: = 13 . QI=0.79K-9.4954Hx - 7.44 (R (R2==0.956);0.979) ; QI=13.54Hx-7.44Hx = 0.06K - 0.13 (R = time. Thus, among the components considered,0 .the950 Hx). T(Rab2l=0.979);e 4 p Hx=0.06K-0.13resents the (Rre2=0.950).sults o Tablef a 4c presentsombined quality value increased linearly with the storage time and cthela slinearsific atitheon resultsof Pa c ofif ic a combinedwhite sh r qualityimp b classificationetween the Q ofIM Pacificand chemical regression equation between Hx and the storage indaydi cwasato rs whiteinclu dshrimping K -betweenvalue a nthed hQIMypo xandan thichemicalne. indicators Hx=0.177×day+0.33 (R2=0.974). The K-value calculated including K-value and hypoxanthine. from the equation increased with time of storage. TheTab linearle 4. Quality classification of white pacific shrimps based on QI, K-value, and hypoxaTablenthin 4.e. Quality classification of pacific white shrimps based on regression equation between the K-value and storage day QI, K-value, and hypoxanthine. was K-value=3.05×day+1.8 (R²=0.992) (Fig. 2).Q Studiesuality c lass QI K-value Hypoxanthine [10-15, 31] also show that the K-value and hypoxanthine Quality class QI K-value Hypoxanthine( (Hx)Hx) Excellent 0≤QI≤2.9 0≤K≤18.36 0 ≤Hx≤ 0.75 amount increase linearly with storage time. This suggests Good Excellent 2.9<Q0≤QI≤2.9I≤8.87 0≤K≤18.3618.36<K≤0≤Hx≤0.7524.30 0.75<Hx≤1.09 that it is possible to use the amount of hypoxanthine to Acceptable Good 8.87<2.9<QI≤8.87QI≤14.12 18.36<K≤24.3024.30<K≤0.75<Hx≤1.0929.34 1.09<Hx≤1.35 assess the quality change of Pacific white shrimps preserved Moderately Acceptable 14.128.87<QI≤14.12<QI≤18.5 24.30<K≤29.3429.34<K≤1.09<Hx≤1.35 34.11 1.35<Hx≤1.72 at 0°C using the linear regression procedure betweenAccep thetab le Moderately acceptable 14.12<QI≤18.5 29.34<K≤ 34.11 1.35<Hx≤1.72 K-value and hypoxanthine presented above. Conclusions A QIM scheme has been developed for Pacific white shrimp Vietnam Journal of Science, (Litopenaeus vannamei) stored at 0°C. The scheme employs the 50 Technology and Engineering June 2021 • Volumedesc 63ri pNtumberive t 2erms for quality changes in sensory attributes in accordance with the quality requirements required by QIM (from 0 to 3). The quality of the shrimp was categorized into four classes, including Excellent, Good, Acceptable, and Moderately Acceptable, which are based on the QI score. The QIM scheme for Pacific white
7. Life Sciences | Agriculture Conclusions [15] Y.R. Huang, M.F.J. Zelaya, C.Y. Shiau (2016), “Changes in biochemical compositions and quality of white shrimp (Litopenaeus vannamei) during A QIM scheme has been developed for Pacific white storage”, Journal of Aquatic Food Product Technology, 25(1), pp.35-45. shrimp (Litopenaeus vannamei) stored at 0°C. The scheme [16] M.J. Leboffe, B.E. Pierce (2015), Microbiology: laboratory theory and employs the descriptive terms for quality changes in sensory Application, Morton Publishing Company. attributes in accordance with the quality requirements [17] D.C. Bernardi, E.T. Mársico, M.Q.D. Freitas (2013), “Quality index method required by QIM (from 0 to 3). The quality of the shrimp (QIM) to assess the freshness and shelf life of fish”, Brazilian Archives of Biology was categorized into four classes, including Excellent, and Technology, 56(4), pp.587-598, DOI: 10.1590/S1516-89132013000400009. 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