High moisture extrusion of plant proteins

Abstract

The main aim of the thesis was to develop and evaluate the meat analogues from alternative protein sources such as soya, lupin and microalgae using high moisture extrusion (HME) processing. In the first part of the work, the effect of extrusion conditions, such as barrel temperature (135–180 °C), water feed (40–68 %) and screw speed (400–1800 rpm) on extruder responses and properties of the meat analogues based on lupin protein concentrate and isolate (50:50) was investigated. Barrel temperature showed negligible influence on the tested properties. A negative linear relationship of water feed was found on all of the extruder responses and on colour difference and cutting force of extrudates. Product temperature at extruder, specific mechanical energy and cooking yield of the extrudates were increased with increased screw speed. An increased in-vitro protein digestibility (IVPD) was observed with higher water feed content. Meat analogues showed better texturization with increased temperature and screw speed along with decreased water content. The investigation further continued with the aim of testing the feasibility of incorporating Spirulina platensis biomass with lupin protein mixtures for HME. The influence of different Spirulina concentrations (up to 50 % by dry mass), extruder barrel temperature (145 °C, 160 °C and 175 °C), water feed (50, 55 and 60 %), and screw speed (500, 800 and 1200 rpm) on the extrudate properties was investigated. The physical properties, such as texture, cooking yield and expressible moisture were significantly affected by the Spirulina addition and extrusion parameters. Increased temperature and screw speed as well as decreased water feed slightly improved the content of total flavonoids, total phenolics and antioxidant activity of meat analogues, and the addition of Spirulina biomass significantly increased those properties. The addition of Spirulina negatively influenced the IVPD of extrudates, however, this effect was counterbalanced with the controlled extrusion conditions, such as increased water feed and screw speed. Furthermore, the extrusion process modified the secondary structural properties of the proteins in the meat analogues. Further, the application of iota (ι) carrageenan (ICGN) as an additive was investigated to develop a soya meat analogue using a planetary roller extruder (PRE). The addition of ICGN significantly increased the cutting force and elasticity and decreased expressible moisture and cooking yield. Additionally, an increase of the compact network structure of the extrudates was observed with the addition of ICGN by the scanning electron microscopy. Sensory evaluation revealed that the meat analogue with 1.5 % ICGN was best accepted, and the addition of ICGN improved the fibrous structure/texturization, which is a key property of the meat analogues.