Elsevier

Food Control

Volume 68, October 2016, Pages 83-91
Food Control

Effect of Citrus wilsonii Tanaka extract combined with alginate-calcium coating on quality maintenance of white shrimps (Litopenaeus vannamei Boone)

https://doi.org/10.1016/j.foodcont.2016.03.028Get rights and content

Highlights

  • Composition profile of the methanol extract of Citrus wilsonii Tanaka.

  • Broad-spectrum antimicrobial activity of the extract of C. wilsonii.

  • Specific bacterium Lysinibacillus sphaericus responsible for the shrimp spoilage.

  • Preservative potential for the shelf life and good quality of the shrimps.

Abstract

The combined effect of Citrus wilsonii extract and alginate-calcium film coating on microbiological, chemical and sensory changes of white shrimps (Litopenaeus vannamei) was studied over 6 days of storage at 4 °C. A specific spoilage microorganism Lysinibacillus sphaericus S1 was isolated from local shrimp samples, which could cause the appearance of orange spoilage spots. The methanol extract of C. wilsonii exhibited significant antimicrobial activity against L. sphaericus S1, as well as several other food-borne pathogens. GC–MS analysis showed a high percent of furandione and furfural compounds in the extract. The extract with edible alginate-calcium coating was effective in delaying the quality deterioration of the shrimps stored at 4 °C. Total viable count of the treated shrimps was more than 10 times lower than the negative untreated control. The lower rate of the increase in pH and total volatile base nitrogen (TVB-N) was also observed in shrimps treated with the extract compared to the control group shrimps. After 6 days of refrigerated storage, shrimps treated with the extract combined with coating had the significant higher sensory score for odor, color and texture. The results suggest that the methanol extract from C. wilsonii may be promising to be developed as a new eco-friendly preservative that might be applied to extend the shelf life of shrimps maintaining good quality.

Introduction

Shrimps are an important source of protein and other nutrients throughout the world. China is one of the leading farming countries of fresh water shrimps in the world. White shrimps (Litopenaeus vannamei Boone) is a popular type of species cultured in China, especially in the southeastern China, owing to its freshness and taste (Fu, Chen, & Wang, 2014). However, because shrimps contain a large amount of free amino acids and other soluble non-nitrogenous substances, serving as digestible nutrients for microbial growth (Dabadé et al., 2015a, Dabadé et al., 2015b), they are easily contaminated by microbes and rapidly deteriorate post-mortem, resulting in notorious change of taste, texture and color, and the subsequent low consumer's acceptability (Nirmal and Benjakul, 2011b, Zhang et al., 2015).

Dabadé, Azokpota, et al. (2015) and Dabadé, Besten, et al. (2015) reported that lactic acid bacteria, Enterobacteriaceae and Pseudomonas spp. are the dominant microbial groups on tropical brackish water shrimp at different storage temperatures. Guo et al. (2013) conducted a survey to determine the bacteriological quality of 32 shrimp samples from 9 different countries, and found that aerobic mesophilic bacteria, psychrotrophic bacteria, coliforms, Enterobacter spp. and Listeria spp. were viable on the samples. Actually, even for the same seafood product, microbial spoilage may occur differently, depending on geographical origin and other factors like fishery season and seafood age, and so on (Gram & Huss, 1996). Specific spoilage organisms lead to relevant indicators of spoilage. In our unpublished previous study, we observed that orange spots in local shrimps' head often appeared during post-mortem storage, which were different from common black spots (melanosis) caused by quinone oxidization (Nirmal & Benjakul, 2011a), and the orangening could even sequentially occur all over the shrimp body. Raw fish products are initially contaminated with various microorganisms, and only a selection of these microorganisms is able to colonize and grow predominantly, which manifests as changes of sensory characteristics (Gram & Huss, 1996). The term “spoilage association” has been used for such a specific microbial community. We deduced that such spoilage association may also be responsible for the appearance of the orange spoilage spots in our study.

Previous studies have been conducted to prolong the shelf life of raw shrimps or other seafoods using natural extracts from plants containing plenty of antimicrobial and antioxidant compounds (Encarnacion et al., 2011, Jayaprakasha and Patil, 2007, Nirmal and Benjakul, 2011a). Among them, the family Citrus is one of the most studied natural antimicrobial preservatives for food applications (Iturriaga et al., 2012, Karabıyıklı et al., 2014). The compositions in Citron extract have been proved to be effective alone or in combined way on reducing and inhibiting the foodborne pathogens, including Aspergillus niger (Wu, Cheng, He, Pan, Yao, & Xu, 2014), Penicillium spp. (Richard R. Stange, Midland, Sims, & McCollum, 2002), Fusarium spp. (Bevilacqua, Campaniello, Sinigaglia, Ciccarone, & Corbo, 2012), Bacillus spp., Staphylococcus aureus, Escherichia coli, Enterobacteraerogenes, Salmonella typhymurium (Mahmud, Saleem, Siddique, Ahmed, Khanum, & Perveen, 2009), and so on. Citrus wilsonii Tanaka is a kind of plant widely distributed in southeastern Asian countries, especially in China, Vietnam, Laos and Burma. Its fruits are larger than lemons and are mainly consumed for its nutrient and well-odor value in many traditional foods and recipes (Zhao et al., 2015). Citrus wilsonii fruits, mostly for the ornamental and traditional medicinal use in China, have been studied scarcely on its antimicrobial activity against the spoilage of shrimps. In our unpublished previous research, solvents with different polarity, including petroleum ether, n-hexane, ethyl acetate, ethanol and methanol, were used to extract the antimicrobial components from C. wilsonii fruits, and the methanol extract presented the greatest inhibitory activity against all tested microorganisms. Thus, methanol was chosen as an extract agent in this study.

Film coating, based on edible polysaccharides like chitosan and alginate containing antimicrobial agents, is useful to maintain stable release of preservatives from the surface of foods to the inside and improve storage stability (Fan et al., 2009, Giménez et al., 2013). Alginate, a hydrophilic polymer of β-d-mannuronic acid and α-l-guluronic acid, can form water-insoluble films as better moisture barriers when crosslinked with multivalent metal cations such as calcium (Olivas & Barbosa-Cánovas, 2008). So in recent years, alginate-calcium film is widely used as carriers of antimicrobial and antioxidant compounds to maintain high concentrations of preservatives on the surface of foods (Aşik and Candoğan, 2014, Lu et al., 2010). Chitosan is another carbohydrate polymer with relative polarity and used commonly in food industry. It may function as moisture-sacrificing agent or moisture barriers (Elsabee and Abdou, 2013, Mohan et al., 2012), contributing to higher water holding capacity and lower drip loss of various samples (Mohan et al., 2012).

Since Citrus wilsonii Tanaka has a good acceptance of odor and potential as natural preservatives to extend the shelf life of investigated products, and so far there is little literature about shrimp preservation using citrus extract after incorporation into alginate-based films, this study was carried out to investigate the composition of the methanol extracts from Citrus wilsonii Tanaka fruits, and evaluate its antimicrobial activity against specific spoilage bacteria for the orange spots on local shrimps in Jiangsu province, China. On the other hand, the effective coating of the extract based on alginate-calcium, compared with the chitosan film, was developed to assess the preservative effect on the microbiological, chemical, and sensory properties of the shrimps.

Section snippets

Samples

White Shrimps (L. vannamei Boone) were purchased from Zhongcai aquatic market in Nanjing, Jiangsu province, China. The average weights were 18–25 g per shrimp. The live and fresh shrimps were packed immediately in a plastic container with ice, and transported to the laboratory within 30 min.

Isolation of spoilage bacteria

Fresh white shrimps were packed in sterile polyethylene bags and stored at 4 °C for about one week until orange spoilage spots appeared. The shrimp muscles (2 g) on the spots were collected aseptically, and

GC–MS analysis of C. wilsonii extract

GC–MS chromatogram of the components in C. wilsonii methanol extract is shown in Fig. 1, and Table 2 lists the identified and quantified components in the extract. Totally 44 components in the extract were identified, which can be divided into several groups including ketones, dione, esters, aldehydes, acids, nitrogen-containing components, and so on. Among the components, 3-methyl-2,5-Furandione was the most abundant compound, of which the relative content was 30.74%, followed by

Conclusions

In the present study, the methanol extraction of C. wilsonii in alginate-calcium coating film was used to extend shelf life and maintain good quality of the shrimps during storage. The treatment of the extraction combined with coating film could markedly inhibit the growth of a specific spoilage bacterium L. sphaericus, and retard chemical deterioration which was reflected by the determination of pH and TVB-N. Furthermore, sensory evaluation confirmed the effectiveness of C. wilsonii extract in

Acknowledgments

This study was supported by grant from National Natural Science Foundation of China (31401534) and Jiangsu Agricultural Technological Innovation Fundation (CX(15)1011).

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