nghiên cứu đánh giá biến động các thông số ảnh hưởng đến chất lượng tôm sú penaeus monodon bảo quản ở 0 oc sau thu hoạch

Developing the method to examine the quality of black tiger shrimp basing on the combination of sensory evaluation and chemical indices. This method proved to be efficient in assessing [r]

HUE UNIVERSITY

UNIVERSITY OF SCIENCE

LE NHAT TAM

INVESTIGATE THE VARIATION OF THE

FACTORS INFLUENCING THE POST-HARVEST

QUALITY OF BLACK TIGER SHRIMP DURING

STORAGE AT 0 OC Summary of PhD Dissertation

HUE, 2018

Major : Organic chemistry

Code: 62 44 01 14

PhD DISSERTATION

Supervisors:

1 Associate professor Tran Thi Van Thi

2 Associate professor Do Thi Bich Thuy

Hue, 2018

INTRODUCTION Aquatic products are important sources of nutrients containing high levels of amino acids, peptides, proteins and other essential nutrients for daily meals The decomposition of aquatic species occurs during preservation by microbial activity and chemical reactions

The method used to evaluate the quality of aquatic products depends

on their characteristics, and the preservation conditions Each method only assessed one stage of change, or one aspect of the preservation process Thus, a combination of different methods is very neccessary to evaluate all changes of aquatic products during storage giving more accurate, and reliable results

Therefore, we carried out the research entitled "Investigate the variation of the factors influencing the post-harvest quality of black tiger shrimp during storage at 0 o C "

In this work, we conducted a study to find out the correlation among sensory, chemical and microbial changes during preservation of shrimp

(Penaeus monodon) Basing on the obtained results, the method using to

classify the quality of tiger shrimp is suggested

2 Research objectives

3 Material

Black tiger shrimp (Penaeus monodon), phylum: Arthropoda,

subphylum: Crustacea, order: Decapoda, family: Penaeidae, genus:

Penaeus, species: Penaeus monodon

4 Methodology

- Methods for assessing the quality of black tiger shrimp: determining

2

total aerobic microorganism (TVC), and QIM

- Quantitative methods of chemical indices: TVB-N, TMA-N,

histamine, hypoxanthine and pH values

- Statistical analysis: using Statgraphics centurion XVI software, linear model by MS Excel (2010)

5 New scientific results

The results indicated some important findings as follows:

+ It is a very first time that histamine and hypoxanthine indices were used to evaluate the shrimp quality

+ Changes in the sensory and chemical qualities of black tiger shrimp were observed during storage at 0 oC

+ The linear regression models between QI score, TVB-N, TMA-N, histamine or hypoanthine with storage time were found

+ The combination of sensory evaluation and chemical methods could

be appled to classify shrimp quality

6 Conclusion

The results of this work provided primary infomation in evaluating the

quality of aquatic products after harvest

CHAPTER 1 LITERATURE REVIEW 1.1 Introduction

Characteristics of black tiger shrimp

Chemical composition of some shrimp species

1.2 Type of spoilage and sensory changes during storage: spoilage is caused by microorganisms, enzymes or chemical reactions

1.3 Quality assessing method: sensory evaluation, chemistry, physics, and microbiology measurement

1.4 Developing QIM for black tiger shrimp: Developing a profile describing quality attributes of black tiger shrimp during storage; establishing QIM assessment, examining quality of shrimp according to QIM; evaluating QIM program

1.5 Quantitative method: high performance liquid chromatography (HPLC); ultraviolet-spectral method

1.6 Some models of quality assessment are based on a combination of different methods

Chapter 2 RESEARCH OBJECTIVES AND METHODS 2.1 Research objectives

- Investigating the correlation between sensory, chemical, and

microbiological changes of tiger shrimp preservation (Penaeus

monodon) during storage at 0 ° C basing on quality indices

- Developing the quality classification scale of tiger shrimp basing on quality indices

2.2 Research content

The research content of the study consisted 5 parts:

- Developing method for assessing the quality of shrimp (Penaeus monodon) by QIM

- Developing quantitative method of hypoxanthine on shrimp by HPLC

- Developing linear regression equations between TVB-N, TMA-N, histamine and hypoxanthine

- Investigating the sensory and chemical changes of black tiger shrimp during storage at 0oC and the correlation between sensory quality and chemical quality

- Developing the quality classification scale basing on sensory and chemical indices

2.3 MATERIALS, CHEMICALS AND EQUIPMENTS

2.3.1.Materials

Black tiger shrimps (Penaeus monodon) were provided by 3 different

farms located in Ca Mau Province, Vietnam Each kilogram of shrimp has from 26 to 30 pieces Shrimps haing defects or shell broken were removed Thirty kilograma of fresh tiger shrimp were harvested, washed with water and then put in 300 polyethylene bags (26.8 × 27.9 cm, Alcoa Inc., Richmond, VA 23261, USA) These bags are placed in styrene boxs with ice and the ratio between ice and shrimp was 1: 2 (w / w) After that, shrimps were tranported to the laboratory within 8 hours Polyethylene bags of shrimps were kept at cold temperature 0°C in the laboratory Figure 2.1 describes the process

2.4.2.1 Sample preparation (according to 2.3.1)

2.4.2.2 Selecting and training the panel

The panel was selected and trained carefully for the sensory evaluation [226]

Steps for organizing the panel:

Step 1: Primary recruitment for the panel

Fig A schematic overview of the experimental study QIM refers to quality index method;

TVB-N refers to total volatile basic nitrogen; TMA-TVB-N refers to trimethylamine nitrogen; His refers to histamine; Hx refers to hypoxanthine, TVC refer to total visible counts

Shrimp was stored at 0

Shrimp harvested from farm (10 kg per farm)

Washed using filtered clean flowing water

Packaged in polyethylene bags

TMA-N

n = 3

Stored in ice in polyethylene boxes

Transported to the laboratory

Step 2: Recruiting according to the requirement

Step 3: Training the testers

Step 4: Final recruitment the testers for official assessment

- Primary recruitment for the panel [110]

20 people participated in the recruitment, and selecting 12 members for the panel

-Training the testers (TCVN 11045: 2015) [239]

During this process, 12 members attended the training sessions and recruitment During this period, six members were considered for the official panel Selectng testers in the official sensory evaluation

-Selecting testers for the official panel (TCVN 11045: 2015)

Six testers having the ability, health and time for the sensory evaluation process were selected.: Guidance on sensory evaluation in laboratory for fish and shellfish [5]

+ Assessment QIM method

2.5 CHEMICAL INDICES MEASUREMENT

2.5.1 Sample preparation

2.5.6 pH

The pH value was performed according to the report of Özogul et al [193]

2.6 EXPERIMENTAL DESIGN

2.6.1 Determining aerobic microorganisms

Experiment 1: Investigating the amount of TVC in black tiger shrimp during storage

2.6.2 Developing QIM and evaluating quality of shrimp according QIM Experiment 2: Developing desriptors

Experiment3: Verificating desriptors by Cata method

Experiment 4: Evaluating shrimp quality every day during storage days, establishing the correlation between QI and storage time

Experiment 5: Evaluating the accuracy of QIM

2.6.3 Investigating the change of chemical indices during storage 2.6.3.1 Sample preparation

2.6.3.2 Measuring the changes in quality indices

Experiment 6: Selecting the method to determine the hypoxanthine content of black tiger shrimp

Experiment 7: Developing the standard curve, recovery efficiency, LOD, LOQ and RSD values

Experiment 8: Evaluating the TVB-N content in black tiger shrimp samples during storage

Experiment 9: Evaluating the TMA-N content in black tiger shrimp samples during storage

Experiment 10: Evaluating the histamine content in black tiger shrimp during storage

Experiment 11: Evaluating the hypoxanthine content in black tiger shrimp during storage

Experiment 12: Determining the pH value of black tiger shrimp during storage

2.7 Statistical analysis

All experiments were carried out 3 times All data were processed by Statgraphics centurion XVI software (P<0.05), MS Excel (2010)

CHAPTER 3 RESULTS AND DISCUSSION

3.1 Results of TVC in shrimp during storage

Fig 3.1 showed the number of TVC in shrimp from the day 1 to 10 There was no difference in TVC during the first 7 days of storage, the average value of log cfu/g was 5.02 The number of TVC at day 8, 9 and

3.2 Developing QIM and evaluating shrimp quality according to QIM 3.2.1 QIM model for quality evaluating of black tiger shrimp

The QIM (Table 3.1) was developed during training panel basing on TCVN 3726-89 [2] and previous reports [4], [22], [91], [291]

Table 3.1 QIM for black tiger shrimp Attribute

Scor

e

Light blue turns to light black 2

Body

Grey blue, slightly yellow, no black

10

No odor, slight ammoniac odor 2 Unpleasant odor, strong ammoniac

3.2.2 Quality changes of black tiger shrimp during storage

Fig 3.2 presented the quality changes of shrimp during storage according

to QIM

Fig 3.2 Linear Regression model between storage time and QI of

shrimp The results indicated that QI had linear correlation with storage days This finding was in accordance with earlier reports (Martinsdöttir

et al., 2001) and [107], [171] According to this obtained equation, we can estimate the shelf life of shrimp

3.2.3 Evaluating the accuracy of QIM

The QIM evaluation process was presented in the experiment 5 Ten shrimp samples were used to test the QIM method The results of estimated storage time and real storage time were shown in Fig 3.3

Fig 3.3 Testing the accuracy of QIM method according to estimated

storage time and real storage time

3.2.4 Quality classification of shrimp by QI According to Hanpong et al [91], the evaluation scale for color, taste and structure of black tiger shrimp stored at 0 ° C was from 1 to 9, where 1= extremly like and 9= extremly dislike The results showed that shrimp preserved from 1 to 2 days was perfect quality, from 3 to 5 days was good quality, from day 6 to day 7 was moderate quality, at day 8 was still acceptable quality After the 8th day, the quality of shrimp was unacceptable Jayaweera and Subasinghe et al [113] found that type 1

shrimp (Penaeus indicus) chilled storage had a shelf life from 1 to 3 days,

type 1 shrimp had shelf life until 7 days, accepted quality till 10 days After 10 days, shrimp was rejected due to poor quality Cann [38] also reported that black tiger shrimp preserved at 0 ° C decreased the quality

of taste from 2 to 4 days and appeared black spots from 6 to 9 days Relly

et al [209] indicated that the quality of shrimp reduced after 2 days of

The results of this work showed that storing black tiger shrimp at 0 °C maintained its fresh attributes until day 4 and the quality changed significantly from day 5 At the 5th day, the decomposition of collagen,

12

protein, amine, lipid and fatty acid occurred Therefore, the changes in color, odor and structure were detected clearly The spoilage symptom appeared at the 8th day According to the obtained results, the shelf-life of black tiger shrimp stored at 0°C was 8 days and the quality classification

of shrimp was shown in Table 3.2

Table 3.2 Quality classification of shrimp by QI

3.3.1 Result selection method

Determining hypoxanthine concentration was conducted as previous report of Kok et al (1993)

Fig 3.4 Linear regression model between peak area and concentration The results of HPLC showed the correlation between the peak area and the concentration The equation of standard curve was y= 126,35x + 10,285 (R2 = 0,9977)

3.3.2.1 Determine LOD and LOQ values

0.01 ppm hypoxanthine standard was used (7 times) to evaluate LOD The value of LOD = 3Cm / T [206], the empirical data was LOD = 3 0.01 / 13.13 = 0.002 ppm, LOQ = 3LOD = 0.006 ppm

3.3.2.2 Determining the relative standard deviation (RSD)

RSD values are determined on 10 standard samples with 1ppp

concentration The RSD value was 5.32%

y = 126.35x + 10.285 R² = 0.9977

0 100 200 300 400 500

0 0.5 1 1.5 2 2.5 3 3.5

S

ppm

14

Fig 3.5 TVB-N concentration during storage

In general, the amount of TVB-N in shrimp was significant difference among storage days TVB-N values increased slowly from day 1 to 4 (6.47 to 11.39 mg/100g, respectively) and leveled up rapidly from day 5 Figure 3.5 showed that the angular coefficients of two linear regression equations representing the correlation between TVB-N content and 2 stages of storage (day 1-4 and day 5-10) were different

3.4.2 TMA-N

TMA-N concentration was measured in experiment 8 The changes of TMA-N in shrimp during storage were shown in Fig 3.6

y = 4.5243x - 8.5678 R² = 0.9907 0

10 20 30 40 50

Fig 3.6 TMA-N concentration during storage

The TMA-N concentration in shrimp was significant difference among storage days (p < 0,05) The change of TMA-N had the similar trend to TVB-N TMA-N increased slowly from day 1 to 4 (0,66 to 1,51 mg/100 g, respectively) and leveled up rapidly from day 5 The TMA-N content reached the maximum value at day 10 with 10,45 mg/100 g

3.4.3 Histamin

Histamin concentration was measured in experiment 9 The changes of histamin in shrimp during storage were shown in Fig 3.7 In general, histamine content in shrimp was significant difference among storage days (p < 0,05)

Fig 3.7 Histamin concentration during storage

y = 0,16x + 0,31 R² = 0,994

0 1 2 3 4

2 4 6 8 10 12

TMA-N

Days

3.4.4 Hypoxanthine

Fig 3.8 showed the hypoxanthine content in shrimp during storage

Fig 3.8 Hypoxanthine concentration during storage

Overall, hypoxanthine content in shrimp increased significantly during storage (p <0.05) The linear regression equation describing the correlation between hypoxanthine content and storage time was y = 0.25x

- 0.23 (R2 = 0.976) where y: the hypoxanthine content, x: the storage time

In comparison with the TVB-N, TMA-N, and histamine, hypoxanthine content increased linearly and there was no difference between the two

periods of storage from day 1 to 4 and day 5 to 10

y = 0.2487x + 0.2282 R² = 0.9709

0 1 2 3 4

0 1 2 3 4 5 6 7 8 9 10 11

Hx

Ngày

Fig 3.9 pH value of shrimp during storage

3.5 Correlation equation between chemical quality indices and QI sensory

Table 3.3 summarized the changes in quality of black tiger shrimp during storage The three indices including TVB-N, TMA-N and

histamine related to bacterial counts, therefore, the concentration of TVB-N, TMA-N and histamine was significant difference in the two periods of storage (day 1 to day 4 and day 5 to day 10) The results indicated that chemical quality indices linearly correlated with the storage time Table 3.4 presented the linear regression equations of quality indices

6.6 6.8 7 7.2 7.4 7.6 7.8

pH

Ngày