Glucono-[delta]-lactone-induced gelation of some meat components at chilled temperatures : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Biotechnology and Bioprocess Engineering at Massey University, Palmerston North, New Zealand
In this study, 1,5-glucono-δ-lactone, was used to achieve acid-induced gelation of meat, myofibrillar protein and myosin at 4°C. The mechanisms of gelation of myofibrillar protein and myosin were investigated. The effects of addition of sodium chloride and tetrasodium pyrophosphate to myosin and myofibrillar protein, with and without 1,5-glucono-δ-lactone, were also studied. In addition, the presence of other phosphates, orthophosphatc, tripolyphosphate and hexametaphosphate, in a myosin system were studied to aid in an understanding of the the observed effects of tetrasodium pyrophosphate on myosin. At about pH 4.5, it was observed that extraction of the A-band of myofibrillar protein occurred. It was suggested that an impregnated composite system of myosin reinforcing the myofibrillar structure had formed. At about pH 4.0, complete extraction of the A-band occurred. Dissolution of the myofibrillar structure was suggested to result in myosin network formation of weaker Young's Modulus than the impregnated composite system. Addition of 1,5-glucono-δ-lactone to myosin resulted in the exposure of hydrophobic sites as the pH decreased and it was suggested that acid-induced denaturation had occurred. Gel formation occurred parallel to denaturation. At pH 4.0, the gel became liquid-like and was suggested to be a result of excess repulsive electrostatic interactions. Hydrogen bonding and hydrophobic interactions were shown to be involved in gel formation, whereas sulfhydryl bonding appeared not to be involved in gelation. Sodium chloride was postulated to enhance gel rigidity through its effects on the isoelectric point of myosin. The inclusion of tetrasodium pyrophosphate resulted in network formation prior to acid-induced denaturation and was suggested to enhance hydrogen bonding. The acid-induced gels appeared to revert to myosin or myofibrillar protein when immersed in quiescent water, a condition where unimpeded diffusion of ions was obtained. However, a slow rate of ion diffusion resulted in the formation of a 'strong', translucent gel which was dense to the point of being effectively impermeable to ion migration. These gels were hypothesized to have formed through the displacement of sodium and potassium ions with protons, enhancing hydrogen bonding. Myosin was observed to have a stronger affinity for sodium than for potassium.