Actinidin treatment and sous vide cooking : effects on tenderness and in vitro protein digestibility of beef brisket : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology at Massey University, Manawatū, New Zealand

Abstract

Actinidin from kiwifruit can tenderise meat and help to add value to low-value meat cuts. Compared with other traditional tenderisers (e.g. papain and bromelain) it is a promising way, due to its less intensive tenderisation effects on meat. But, as with other plant proteases, over-tenderisation of meat may occur if the reaction is not controlled. Therefore, the objectives of this study were (1) finding a suitable process to control the enzyme activity after desired meat tenderisation has been achieved; (2) optimising the dual processing conditions- actinidin pre-treatment followed by sous vide cooking to achieve the desired tenderisation in shorter processing times. The first part of the study focused on the thermal inactivation of actinidin in freshly-prepared kiwifruit extract (KE) or a commercially available green kiwifruit enzyme extract (CEE). The second part evaluated the effects of actinidin pre-treatment on texture and in vitro protein digestibility of sous vide cooked beef brisket steaks. The results showed that actinidin in KE and CEE was inactivated at moderate temperatures (60 and 65 °C) in less than 5 min. However, the enzyme inactivation times increased considerably (up to 24 h at these temperatures) for KE/CEE-meat mixtures, compared with KE/CEE alone. The thermal inactivation kinetics were used as a guide for optimising actinidin application parameters during the second phase of the study. For the final experiments, beef steaks were injected with 5 % (w/w, extract/meat) of CEE solution (3 mg/mL) followed by vacuum tumbling (at 4 °C for 15 min) and cooking (at 70 °C for 30 min) under sous vide conditions. This cooking time was considerably less than usual sous vide cooking times used in the meat industry. The actinidin-treated meat had no change in pH and colour, but showed a lower instrumental shear force; and improved sensory scores for tenderness, juiciness and flavour than the untreated meat steaks when tested by a sensory panel. Improved tenderness agreed well with the Transmission Electron Microscopy (TEM) results that showed considerable breakdown of the myofibrillar structure, particularly around the Z line. The addition of actinidin enhanced the rate of breakdown of muscle proteins, as shown by Tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and led to an increase in both protein solubility and ninhydrin-reactive free amino N release, during simulated gastric digestion. These results demonstrate the positive effects of actinidin on meat tenderness and meat protein digestibility during gastric digestion in vitro.