High temperature-shear processing of plant and dairy proteins for the development of structured meat analogues : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Palmerston North, New Zealand. EMBARGOED until further notice.

Abstract

Structural and techno-functional properties of some plant proteins can be transformed into fibrous structures while undergoing high-temperature shear processing (HTSP). However, plant-based substitutes are generally considered to be nutritionally and sensorially inferior to muscle food. Blending dairy protein with plant protein during the restructuring process could improve the functional and nutritional characteristics of the hybrid blend. This study aims to create nutritionally enhanced hybrid meat analogues (HMAs) from plant and dairy protein combinations using an innovative HTSP technique, and investigate the effect on structural, sensorial and nutritional properties of these combinations. The role of protein–protein interactions responsible for fiber formation in concentrated binary protein mixtures undergoing HTSP was also studied. Results indicated that the temperature range of 120°C–140°C, a processing time of 10 min–30 min and a shear rate of 25%–75% (i.e., 806-2314 RPM) create anisotropic structures in soy protein isolate (SPI) and wheat starch (WS) (at a 90:10 ratio) dispersions. Moisture content, shear rate and processing time significantly affected the textural responses (p < 0.05). Interestingly, in the absence of mixing (shear rate ~ 0), no network was formed in protein mixture, suggesting that combined thermal and shear forces were essential to introduce physicochemical changes in protein dispersions. Consequently, the HTSP of SPI, pea protein concentrate (PPC) and plant–dairy protein combinations (using sodium caseinate [NaCas], calcium caseinate [CaCas], whey protein concentrate [WPC] and milk protein concentrate [MPC]) result in various structural morphologies such as gels, layered gels, layered fibrous or fibrous structures. Further, incorporation of 10 % WS in hybrid protein mixtures undergoing the HTSP, enhanced the fiber formation. Restructured mixtures containing 20% MPC and 10% starches (i.e., wheat starch [WS]) combined with plant proteins (35% soy and 35% pea protein mixtures) generated anisotropic structures with textural attributes very similar to “chicken breast”. Therefore, this combination was considered the best formulation for further experimentation and product testing. The effects of material composition and processing conditions on mechanism of fiber formation in novel meat analogues during HTSP and its impact on texture, macrostructure, protein interactions and protein conformations were analysed. We find that the evolution of fibers depends upon the interrelations between shear work input and processing conditions during HTSP. Processing time, moisture content, shear rate and raw material formulation significantly affect HMA energy input, texture and colour (p < 0.05). Both non-covalent (hydrogen, hydrophobic) and covalent (disulphide) interactions during HTSP were responsible for sample structure. However, processing conditions had an insignificant influence on protein–protein interactions. A significant correlation between processing parameters, texture attributes, protein solubility and secondary protein structures of meat analogues was observed. Therefore, a subtle balance of processing conditions and material properties could achieve a fibrous structure with controllable textural and structural functionality in novel meat analogues. The impact of dairy protein (0%, 10%, 20%, 30% and 40% MPC) integrated with plant proteins on physicochemical, sensory and nutritional properties of HMAs were also investigated. The results showed that plant and dairy protein ratios significantly influence HMAs’ textural properties. Meat analogues with 20% MPC are closest in terms of both textural and microstructural properties to boiled chicken. Hybrid samples with 20% and 40% MPC yield acceptable sensorial scores, although overall palatability decreases with increasing MPC concentration. The tenderness and juiciness scores were higher for the hybrid samples than for the plant-only and commercial samples. Nutritional studies showed that essential amino acid (EAA) content in hybrid mixes was higher than in the plant-only meat analogue, indicating enhanced dietary properties.