Chitin extraction from shrimp shell waste using Bacillus bacteria

https://doi.org/10.1016/j.ijbiomac.2012.08.034Get rights and content

Abstract

The ability of six protease-producing Bacillus species (Bacillus pumilus A1, Bacillus mojavencis A21, Bacillus licheniformis RP1, Bacillus cereus SV1, Bacillus amyloliquefaciens An6 and Bacillus subtilis A26) to ferment media containing only shrimp shell waste, for chitin extraction, was investigated. More than 80% deproteinization was attained by all the strains tested. However, demineralization rates not exceeding 67% were registered. Cultures conducted in media containing shrimp shell waste supplemented with 5% (w/v) glucose were found to remarkably promote demineralization efficiency, without affecting deproteinization rates. The antioxidant activities of hydrolysates, at different concentrations, produced during fermentation in medium supplemented with glucose, were determined using different tests: 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging method, reducing power assay and chelating activity. All hydrolysates showed varying degrees of antioxidant activity. Hydrolysate produced by B. pumilus A1 exhibited the highest DPPH radical scavenging activity, with an IC50 value of 0.3 mg/ml. Highest reducing power (DO 700 nm = 1.55 at 1.5 mg/ml) and metal chelating activity (98% at 5 mg/ml) were obtained with B. pumilus A1 and B. licheniformis RP1 hydrolysates, respectively.

Introduction

The waste generated during the industrial processing of shrimp is about 40–50% of its total weight depending on the species, and consisting of heads, shells and tails [1]. Due to the increased world production and consumption of shrimp [2], the seafood industry is focused on an appropriate destination and/or reuse for this waste, since its improper disposal causes serious environmental problems; in fact, this waste is highly perishable and is owing chiefly to the action of microorganisms that there find an excellent growth medium.

Numerous high value by-products from shrimp wastes could be recovered such as carotenoides [3], chitin [4], and proteins [5]. Among various by-products, chitin is a water insoluble polysaccharide constituted substantially of β-(1  4) linked N-acetyl-d-glucosamine units [6]. This natural biopolymer exists widely in crustaceans, insects, and microorganisms and has wide potential applications in different areas.

Shrimp chitin can be extracted by chemical [7], physical [8], enzymatic [9], [10], or microbiological [11] methods. The use of corrosive chemical agents such as strong acids or bases makes the process of chitin extraction ecologically unacceptable [12]. Recovery of chitin by biotechnological process from crustacean shell waste consists of two fundamental steps: protein degradation or deproteinization and demineralization. Accelerated hydrolysis, accomplished by the use of commercial or microbial proteases, has many advantages since it allows the control of the hydrolysis and thus minimizes undesirable reactions. However, demineralization has been done using HCl, either after or previous to enzymatic deproteinization step [13].

As a substitute to the chemical and enzymatic processes, fermentation, combining deproteinization and demineralization, has been evaluated as an eco-friendly and positive procedure [14]. Furthermore, fermentation represents a cheap technique which will stabilize and retain the nutritional quality of by-products [15].

Fermentation has been used for prawn [16], crab [17], squid pen [18], oyster [19], scampi [20] and shrimp by-products [12].

The objective of this research was to study the effect of six protease-producing strains on the fermentation efficiency of shrimp shell biowaste for chitin recovery. Antioxidant activities of the hydrolysates obtained during fermentations were also investigated.

Section snippets

Shrimp shell waste

The shrimp (Metapeneaus monoceros) shells were procured in fresh condition (in a cool box) from a shrimp processing plant located at Sfax, Tunisia, and consisted of heads, thoraxes and appendixes. The waste was washed, then minced through a 2 mm sieve using a meat mincer, and stored at −20 °C.

Microorganisms and preparation of inoculation

Six protease-producing Bacillus strains were tested for their ability to ferment media consisting of shrimp shell waste. The stains used were Bacillus cereus SV1 [21], Bacillus subtilis A26 [22], Bacillus

Results and discussion

The application of microorganisms or proteolytic enzymes for deproteinization of marine crustacean wastes is a current research trend in conversion of wastes into useful bioactive substances. It is a simple and environment-friendly alternative to chemical methods employed in the chitin preparation process.

In this study, the performance of six Bacillus species in the deproteinization and demineralization efficiencies of shrimp shell waste for chitin extraction was studied.

Conclusion

In the present study, two bioactive materials (chitin and antioxidant) were recovered from shrimp shell waste after fermentation using six Bacillus strains. High deproteinization rates were achieved by all the strains tested when cultivated in medium supplemented or not with glucose. Glucose supplementation was found to improve demineralization. Moreover, shrimp waste hydrolysates recovered from liquid fermentation fractions, have proved to possess varying antioxidant activities.

Further works

Acknowledgment

This work was funded by the Ministry of Higher Education and Scientific Research, Tunisia.

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