Hydrolysis of chicken intestine for flavor development in cat food

Abstract

Increasing number of chicken slaughterhouse in Malaysia has produced a tremendous amount of waste that can be potentially utilized as a source for manufacturing a value added product. However, due to lack of scientific study, the waste is normally discarded which may give negative impacts to the environment. Thus, this study focuses on utilizing by-product from poultry industry such as chicken intestine for chicken flavour development, which cysteine and methionine are the precursor for the chicken flavour. In this study, chicken intestines were firstly characterized and their shelf life were studied before being hydrolysed using chemical and commercial enzyme protease to obtain chicken flavoured hydrolysate. Raw chicken viscera show significant amount of crude protein 9.1% w/w and crude fat 3.0% w/w. It was observed that fresh intestines have the highest protein content 8g/L while storage at -20°C sustained the protein concentration up to 88%. In contrast, storage at 0°C reduced the protein concentration for about 28% and 50% following one and two weeks of storage, respectively. Three different conditions of hydrolysis were studied; i) hydrolysis with indigenous protease without adjusting pH, ii) hydrolysis with indigenous protease with pH adjusted to 2.8 using 1N HCl and iii) hydrolysis with addition of 1% (v/v), 2% (v/v), and 3% (v/v) commercial protease. Results from this study showed that hydrolysis using 1N HCl at initial pH 2.8 produced protein content 19.12% higher than hydrolysis without pH adjusted where the initial pH recorded was 6.3. Meanwhile, hydrolysis using 1% (v/v), 2% (v/v) and 3% (v/v) commercial protease at buffer pH 6.4 produced protein content ranging from 3.85 g/L to 5.05 g/L, which the highest protein concentration was obtained from hydrolysis with addition of 2% (v/v) commercial protease. In addition, the detection of cysteine and methionine as precursor for chicken volatiles known as 2-methyl-3-furanthiol and 2-methyl-3- furanthiol using HPLC confirmed the production of the chicken flavour. From this study, it could be concluded that the highest amount of cysteine (0.44 mg/mL) and methionine (0.67 mg/mL) produced are from hydrolysis with indigenous protease with pH adjusted to 2.8 using 1N HCl and could be potentially used as key ingredients in developing chicken flavour for cat food industries. With thorough optimization, this research will benefit the rapidly-growing cat food industry in Malaysia.