Deodorisation of protein hydrolysate and extraction of proteins from Hoki (Macruronus novaezelandiae) skin : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology at Massey University, Albany, New Zealand
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The present study had two main objectives. The first objective was to identify a suitable deodorisation treatment for pre-prepared Hoki skin protein hydrolysate (HSPH) and the second objective was to investigated suitable pre-treatment and extraction processes for collagen and gelatine from Hoki (Macruronus novaezelandiae) skin which resulted in low odour extracts. The off-odour in HSPH post-deodorisation treatments and in the Hoki collagen and gelatine post-extraction processes were assessed by determining the total volatile base nitrogen (TVB-N) and trimethylamine (TMA) concentrations. The sensory technique of flash profiling was employed to determine the odour attributes in all HSPH, gelatine and collagen samples after treatment and extraction processes. In addition to the respective off-odour assessments, the extracted collagen and gelatine were evaluated in terms of total protein content (g protein/100g dry sample), moisture content (w/w%), and yield (w/w% of dry sample). Sodium dodecyl sulphate- polyacrylamide gel electrophoresis (SDS-PAGE) was conducted to determine the molecular weight (kDa) of extracted collagen and gelatine. Amino acid profile analysis was performed to identify the extracted samples. In the first part of this study, dried green tea leaves (GT), powdered tea polyphenol (TP) and dried olive leaves (OL) investigated for deodorisation of HSPH. Using an orthogonal design, three factors (concentration, temperature and time) and three corresponding levels were used in the design. The two most suitable deodorisation treatments for pre- prepared HSPH were 1) deodorant: powdered tea polyphenol; concentration: 0.04 g/ml hydrolysate; temperature: 50˚C; time: 20 min, and 2) deodorant: powdered tea polyphenol; concentration: 0.04 g/ml hydrolysate; temperature: 80˚C; time: 60 min. For a more economical solution, GT was determined to be a possible alternative deodorant to TP by manipulating the total phenolic content prior to deodorisation. For a secondary deodorisation treatment, preliminary results on strong acid hydrogen form ion exchange resin (Dowex G-26) reduced the TMA concentration in partially deodorised HSPH sample significantly (p-value<0.05) from 3.4±0.1 deodorisation to 0.8±0.1 mg of nitrogen/100g wet sample. In the second part of this study, Hoki skins were pre-treated using 0.2 M NaOH solution (1:6 w/v) for 60 min at 18±2oC and then extraction with distilled water (1:10 w/v) for 60 minutes at 50±2˚C. This treatment produced gelatine product with the highest protein content (41.3±0.9 g of protein/100g dry sample) and reduced off-odour based on TMA content (0.9±0.1 mg of nitrogen/ 100 g wet sample). However, a lower gelatine yield recovery of 61.0±1.7 % was determined in this gelatine sample. SDS-PAGE and amino acid profile tests concluded that all pre-treatment and extraction processes successfully extracted gelatine samples as the final product. In contrast, collagen samples were not confirmed as pure collagen in this study. The current findings for both objectives of this study has shown that pre-treating the raw material using acid or alkali prior to subsequent processes is more efficient in reducing the off-odour in the final products rather than employing deodorisation processes as a subsequent countermeasure after hydrolysis and extraction.
Hoki, Deodorization, Protein hydrolysates, Extraction (Chemistry), Oils and fats, Odor control