Update:
Reporting Period: July 1 – Dec 31, 2022
Plant-based meat analogues and other alternative protein products have become increasingly popular in recent years as the number of “flexitarian” consumers increases. Plant-based meat retail sales recently exceeded $5 billion with consumers wanting nutritious, affordable, sustainable and tasty products. With these goals, challenges arise such as the ability to accurately mimic the texture and other important sensory aspects of a meat product.
In this reporting period, research was focused on investigating the use of soy protein and other complementary plant protein physico-chemical properties including swelling and gelling characteristics for design of meat analogues targeting certain applications, such as a plant-based beef burger or fish patties.
Many of these physico-chemical properties relate to hydration and water solubility of plant proteins, which have been identified in preliminary research by our team to be important functionality attributes that affect texture of the final product. Proteins can be characterized as either heat gelling/ swelling or cold swelling based on their solubility in the presence or absence of heat. Cold swelling proteins have been shown to be more “functional” and lead to greater degree of cross-linking, texturization and expansion of the final texturized vegetable protein (TVP) product causing a softer and spongier final texture. On the other hand, heat swelling proteins are less functional and lead to a denser and more layered TVP.
Experimental work was primarily based on soy protein (isolate, concentrates and flour), but other protein sources including pea protein isolate and wheat gluten were also used for their potential to modulate product properties. All plant proteins were analyzed for cold water swelling and heat gelation properties using physico-chemical tests such as water absorption index (WAI) and least gelation concentration (LGC). These tests allowed proteins to be categorized as cold or heat swelling, based on which six formulations (or treatments) were designed for extrusion processing with specific ratios of cold/heat swelling proteins (0:100, 30:70, 40:60, 50:50, 60:40 and 90:10) to target textures mimicking beef or fish analogues. It was hypothesized that higher the cold/ heat swelling ratio, the softer would be the product texture. Three of the treatments were designed to target a firmer beef burger texture and another three for softer textured fish patties. Details of the experimental treatments are provided in Table 1 (see supplementary data document). The treatments included formulations with soy only, and combinations of soy and pea proteins, and soy and wheat proteins. For a firmer beef analogue texture, protein content in the range of 65-70% and higher amounts of heat swelling proteins such as Arcon F soy protein concentrate and wheat gluten were used to yield swelling ratios in the range of 0:100 to 50:50. For a softer and flakier fish analogue texture, protein content in the range of 70-80% and higher amounts of cold swelling proteins such as soy protein isolate, Arcon S soy protein concentrate and pea protein isolate were used to obtain swelling ratios in the range of 40:60 to 90:10. Modifying ingredients such as carbohydrates (example, tapioca starch) have been shown in previous studies by our team to help for further modulation of TVP texture as they tend to interrupt protein cross-linking during extrusion processing and increase layering.
Pilot-scale twin screw extrusion (model TX52, Wenger Manufacturing, Sabetha, KS) was used to produce texturized vegetable protein (TVP) products using the above mentioned 6 formulations. A ¼ inch venturi die was used to increase shear and mechanical energy to improve texturization of the plant protein materials. The final discharge die contained 2 openings that were each ¼ inch. Extrusion processing data were recorded twice for each treatment at the beginning and end of the collection time and was also collected using a data acquisition system every second. The texturized product was cut after exiting the extruder by 3 hard rotating knives. Part of the product after exiting the extruder was immediately dried at 225oF for 16 minutes followed by cooled for 8 minutes in a continuous gas-fired drying/ cooling system (Wenger Series 4800). Rest of the product was taken directly off the extruder and ‘wet milled’ using an Urschel mill with a screen size of 0.18 in. Dried TVP was tested for bulk density and water holding capacity (WHC). The milled product was formed into patties using binders, and a preliminary evaluation was conducted for textural attributes such as firmness (versus softeness) and chewiness.
For optimum texturization, highest pre-conditioner water input during extrusion was required for treatments based on soy only, followed by soy/ wheat and the lowest for soy/ protein, resulting in in-barrel moisture content of 47-48%, 42-44% and 38-40% wet basis, respectively. This was consistent with the highest viscosity typically observed for soy proteins and lowest by pea proteins. Viscosity controls the extrusion specific mechanical energy (SME) input, which is required to an adequate level for protein cross-linking and texturization. However too high energy input can lead to a over processed or even burnt product. Extruder screw speed was also varied for each treatment (300-449 rpm) to fine tune the SME input and residence time and obtain optimally texturized product. Overall, SME ranged from 875-997 kJ/kg (Figure 1, supplementary data document). The die temperature was highest for soy only treatments (160-165oC), followed by soy/ wheat (150-165oC) and lowest for soy/ pea (150-160oC). It was interesting to note that lower cold/ heat swelling ratio led to higher die temperatures, in general.
WAI of raw ingredients decreased from 5.61 to 2.51 as cold swelling proteins in the formulation decreased. Extruded TVP bulk density increased from 157 to 295.2 g/L and WHC decreased 5.25 to 2.73 with increase in proportion of heat swelling proteins. These data along with textural data were in accordance with previous work that signaled heat swelling proteins create denser, more layered and firmer products while cold swelling proteins lead to porous and softer products. Initial sensory data showed that optimal plant-based ‘beef’ patties with the right chewiness and springiness were based on combination of soy proteins and wheat gluten, while optimal plant-based ‘fish’ patties were based on soy proteins only.
As next steps, further physico-chemical testing of raw materials will be conducted including rapid visco analysis and also the chemistry of the plant proteins will be evaluated using methods such as SDS-PAGE. Final TVP product and patties will be further evaluated using texture profile analysis, and focus group and consumer acceptance studies will also be conducted. Ingredient cost and other input costs will also be used to conduct an economic study.
View uploaded report 