Improvement of gel properties of sardine (Sardinella albella) surimi using coconut husk extracts

Highlights

• Coconut husk ethanolic extracts affected textural properties of sardine surimi gel.

• E60 and E80 at optimum levels enhanced breaking force and quality of surimi gel.

• E60 and E80 had no negative effect on sensory property of sardine surimi gels.

Abstract

Effects of coconut husk ethanolic extracts on gelling properties of surimi from sardine (Sardinella albella) were investigated. Extracts prepared using 60% ethanol (E60) and 80% ethanol (E80) with total phenolic content of 464 and 454 mg tannin/g, respectively, were incorporated into surimi gel. Gels added with E60 or E80 had the increases in breaking force as the levels increased and the highest breaking force was observed when added with 0.125% E60 or 0.075% E80 (p < 0.05). Both E60 and E80 had no detrimental effect on sensory attributes of surimi gel. However, slight decrease in whiteness was found in gel added with the coconut husk extracts. Electrophoretic studies showed that disappearance of myosin heavy chain took place when incorporated with both E60 and E80, regardless of levels used. Lower autolysis of surimi gel was found in the presence of both extracts. Addition of E60 and E80 could increase the cross-linking of proteins during heating as indicated by the higher G'. The microstructure study revealed that surimi gel added with coconut husk extracts had higher strand density and connectivity than the control gel. Thus, coconut husk extracts at an appropriate level could improve gel strength of sardine surimi with an increased acceptability.

Introduction

Coconuts are abundant in coastal areas of tropical countries including Thailand. During processing, the husk of coconut is removed and the millions of tons of husk are generated each year (Panyakaew & Fotios, 2011). The husk is mainly composed of lignin and cellulose, which are dietary fibre and recommended as GRAS (Woods & Gorbach, 2001). Additionally, husk is rich in phenolic compounds, namely 4-hydroxybenzoic acid (4-HBA), ferulic acid, tannic acid as well as lignin phenols such as vanillic acid, ρ-coumaric acid and syringic acid (Lobbes et al., 1999, Rodrigues and Pinto, 2007). Phenolic compounds have been known to possess antioxidant (Maqsood, Benjakul, & Balange, 2012), antimicrobial and antiviral (Carvalho et al., 2013, Hossain et al., 2014) and anticancer activities (Gawlik-Dziki et al., 2012). Furthermore, the use of phenolic compounds has been extended as a protein cross-linking agent, particularly in the oxidised form (Balange & Benjakul, 2009a).

Surimi, the washed fish mince, has gained popularity as raw material for preparing several products with elastic texture (Mansfield, 2003). Generally, lean fish are commonly used for production of surimi since they yield surimi with white colour and better gel properties as compared to dark fleshed fish. Due to the insufficient lean fish, pelagic dark-fleshed fish such as sardine (Sardinella albella) and mackerel (Rastrelliger kanagurta), have been used as alternative raw material for surimi production (Arfat & Benjakul, 2001; Chaijan, Benjakul, Vissessangan, & Faustman, 2004). Nonetheless, those pelagic dark-fleshed fish have high lipid, myoglobin and sarcoplasmic protein contents, which contribute to the difficulties in making high-quality surimi (Chaijan, Panpipat, & Benjakul, 2010). Dark-fleshed fish also contain high level of proteases, particularly heat-activated proteases, which show an adverse effect on gel formation (Hu, Morioka, & Itoh, 2010). Those proteases have been reported to induce the degradation of myofibrillar proteins associated with gel weakening. These limit the use of dark-fleshed fish as raw material for production of surimi and other products.

To tackle such a drawback, various food-grade additives and cross-linking enzymes such as microbial transglutaminase have been used (Kaewudom et al., 2013, Oujifard et al., 2012). Balange and Benjakul, 2009a, Balange and Benjakul, 2009b reported that oxidised phenolic compounds, such as oxidised tannic acid or ferulic acid, could increase breaking force and deformation of surimi from bigeye snapper and mackerel. However, the oxidation of phenolic compound from ortho-diphenol into ortho-quinone form, either enzymatically or by molecular oxygen, could negatively affect the quality of some food products by decreasing desirable aroma, and lowering antioxidant activities (Nikolantonaki, Magiatis, & Waterhouse, 2014). Since phenolic compounds are rich in hydroxyl groups, surimi gel can be strengthened via hydrogen bond and other interactions (Ali, 2002). Extracts from coconut husk containing phenolic compounds could be used as natural protein cross-linker possessing antioxidant activity. The present study aimed to investigate the effect of coconut husk extracts on the properties of surimi gel from sardine, an abundant dark fleshed-fish in the Southern Thailand.