Manufacture of cooked meat reaction flavour from mixed hydrolysates of lambskin and wool : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology at Massey University, Manawatu, New Zealand
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2024
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Massey University
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Abstract
The proposition was explored that woolly lambskin could be a useful substrate for cooked meat flavour production, in admixture with a suitable sugar source, both acting as Maillard precursors. This thesis explored making a thermal hydrolysate of collagen from the lambskin and an enzymatic hydrolysate from wool then combining the two extracts in a reaction mixture for flavour production and assessment. Proximate analysis of raw dewooled lambskin indicates its major components as moisture (75%) and crude protein (21%). Thermal extraction was initially conducted in steam at 5 psi (0.34 bar.g) pressure at various pH values. The maximum degree of solubilisation of solids was obtained at a pH of 3.55. A pH value of 4.5 was chosen for subsequent thermal hydrolysis, as further reduction in pH to 3.55 consumed large amounts of sulphuric acid. Thermal hydrolysis of lambskin was further explored at pH 4.5 to obtain collagen hydrolysates at three industrially convenient temperatures, 90°C, 108°C, and 121°C. The maximum degree of solubilisation of 89.3% was obtained for the lambskin treated at 121°C for 10 hours. Degree of solubilisation did not increase greatly with increases in temperature and time from 90°C to 121°C and from 2 hours to 10 hours. The optimal treatment condition from a process perspective was judged to be 108°C for 2 hours with a degree of solubilisation of 85%. The thermal hydrolysis itself was successful in producing collagen hydrolysates with low viscosity in the range of 2.2 to 5.6 mPa.s, which was measured using a Modular Compact rheometer at 40℃ and 11°Brix. The viscosity of the extract decreased as expected with an increase in treatment time. The degree of hydrolysis (DH), an indirect measure of the peptide chain length of the hydrolysate produced, was estimated based on the ninhydrin test. The DH increased from 26% to 37% with an increase in the processing times tested. The increase in the degree of hydrolysis indicates that smaller molecular peptides are formed, which in turn reduces the viscosity of the sample. Proximate analysis indicates that wool removed from lambskin is composed of 94.6% crude protein. Almost thrice the stoichiometric amount of sodium metabisulphite was used for sulphite pretreatment to soften the wool. Sulphite-treated wool was hydrolysed using the enzymes Neutrase® 0.8L, Alcalase® 2.4L FG, and Protamex®. The maximum degree of solubilisation of wool solids (50%) was obtained using Alcalase® 2.4L FG at an enzyme-to-substrate ratio of 3:100 at pH 7.5. Reaction mixtures were then prepared by mixing an organic sulphur source, ribose, and lambskin extract concentrated to 60°Brix. The ratio of organic nitrogen to organic sulphur was kept constant across all the reaction mixtures at about 10.6, whereas the ribose to collagen ratio was kept constant at 1:8. The organic sulphur sources trialled were cysteine, cysteic acid, sulphite assisted hydrolysate from wool, and alkali-assisted hydrolysate of wool (as a source of lanthionine). Sensory analysis of the samples by 25 untrained panellists confirms that cysteine is important in creating a meaty flavour profile. Sulphite-assisted hydrolysate from wool had the most pungent and animal-like flavour profile. Alkali-assisted hydrolysate of the wool, and hence lanthionine is not useful in creating flavours as the flavour note was very mild. Cysteic acid resulted in a burnt and caramel flavour note. This work did not liberate sufficient reactive cysteine from wool to indicate that woolly lambskin offers a useful meat flavour substrate.
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