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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Date
2018
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Massey University
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Abstract
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.
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Keywords
Hoki, Deodorization, Protein hydrolysates, Extraction (Chemistry), Oils and fats, Odor control