January 5, 2016—Characteristics & uses of extruded plant proteins are many and varied, given that vegetable proteins can be texturized and extruded into different shapes, forms and uses for a variety of applications. In some cases, this provides a more feasible option to increase the protein content of a food than working directly with the food matrix. While many plant protein sources can be used for texturized vegetable protein (TVP) products, soy is the most common. About 80-90% of the TVPs found in the market place today are soy-derived.
Other proteins that can be texturized include wheat, peanut, chick pea, green pea, lentil and yellow pea. But, “in order to create TVPs, the functionality, composition and behavior of the proteins used must be understood,” explained Mian N. Riaz, Ph.D., Director, Food Protein R&D Center, Texas A&M University, in his presentation “Processing, Characteristics and Uses of Extruded Plant Protein Ingredients.”
For example, vital wheat gluten is the primary protein component in wheat-based raw materials. It is very hydroscopic and sticky. Pea protein concentrate, with 46% protein, would typically also contain 17% starch, 18% sugars, 4% ash, 2.7% oil and 2% crude fiber. In contrast, a faba bean protein concentrate of 63% protein may contain only 0.1% crude fiber.
Soybeans can be made into flour, soy protein concentrate, grits or flakes. The process is very complex, with extractions, purification and concentration. Alterations in any step can impact the finished ingredient—and every process adds cost—which explains why soy protein isolates and concentrates are so expensive.
“Because of their higher cost, soy concentrates and isolates are rarely used alone in TVPs,” Riaz said. However, their addition improves water-holding capacity and protein content. There are at least 23 different types of soy protein concentrate for different applications, so it is important to specify the application to the vendor. The goal is to understand the functionality of the raw materials to give good texturization, he added.
It is essential to know the protein level, protein dispersibility index (PDI), nitrogen solubility index (NSI), oil and fiber content, and particle size of the raw materials. All of these properties affect texture in the finished product. Higher protein levels give firmer-to-rubbery textures. For example, at a 90% protein level, a very rubbery texture occurs, which is not desired. For textured vegetable protein products, ideally, protein should be about 50- 60% for a very good texture.
PDI and NSI are measures of a protein’s solubility in water and are related to the amount of heat treatment. “The PDI test is more rapid and tends to give slightly higher results than NSI,” said Riaz.
The ideal place to start for good texture is about 60 PDI. This attribute also affects color, with a higher PDI being lighter in color. Darker soy ingredients are typically used for feed, while lighter are used for human food products. Riaz continued to explain: “Oil and fiber content reduces [the] protein level by dilution and interferes with texturization. Soy hull fiber can cross-link with protein macromolecules, affecting structure and texture; typically, in these products, less fiber is better.”
When creating TVPs, native-state proteins are preconditioned with steam and water, where they begin to swell and unfold, and then cross-link during the extrusion process. Extrusion changes ingredients chemically and physically, and a new material is created.
An extruder is a continuous pressure-cooker to which water and raw materials are added, and temperature is increased within seconds. Depending on the type of extruder, there are many functions it can perform. Different protein products can be created, including chunk-style, shredded or structured meat analogs in any shape, size or cut.
For chunk, minced and flaked textured soy protein products, Riaz advised to use soy flour with 60-70 PDI, and 50-55% protein content. “Important properties include water absorption, oil absorption and a meat-like texture. Color can be added to make it look like beef or chicken, and flavors can also be used,” Riaz continued.
Meat analogs can look and behave just like any kind of meat with similar appearance, texture, water absorption and rehydration time. Cooking characteristics are also similar to meat. Applications include vegetarian diced-meat dishes, stew meat, jerky, barbecue, pot pie, pasta and more.
Mian N. Riaz, Ph.D., Director, Food Protein R&D Center, Texas, A&M University, mnriaz@tamu.edu
The summary above is an excerpt from the “2015 Protein Trends & Technology Magazine: Formulating with Proteins.”
