Penn State uses lentil protein to restore full-fat texture in nonfat yogurt

Penn State researchers have used modified lentil protein to give nonfat yogurt mechanical properties comparable to those of whole-milk yogurt, adding just 0.05% of the ingredient to nonfat milk before yogurt production.

• Enzymatic treatment broke lentil protein into smaller polypeptides capable of mimicking some of fat’s textural functions.
• The best-performing material held more than four times as much oil as unmodified lentil protein.
• At 0.05% inclusion, the ingredient improved yogurt gel formation and mechanical texture.

The study, published in Food Chemistry, examined whether breaking lentil protein into smaller pieces could produce a functional ingredient for foods that lose structure when fat is removed. The researchers found that a partially hydrolyzed protein preparation strengthened the yogurt gel, improving properties associated with firmness, elasticity and resistance to deformation.

The findings address a familiar formulation problem. Removing fat changes more than a product’s calorie content. In yogurt, it also affects thickness, lubrication, structure and mouthfeel, leaving manufacturers with several properties to recover if a nonfat version is to resemble its full-fat equivalent.

Yi Zhang, the study’s senior author and Frederik Sr. and Faith E. Rasmussen Career Development Professor in Food Science at Penn State’s College of Agricultural Sciences, said existing ingredients do not always meet that requirement.

“Although commercial fat replacers reduce calories, they often fail to replicate the functional and sensory qualities of fat,” she said.

“There has not been much research done on plant protein–based fat texturizers, showing the need for novel fat texturizers derived from plant proteins that are low-calorie, cost-effective and have excellent functionalities across diverse food applications.”

The team used alcalase, an enzyme that breaks down proteins, to partially hydrolyze lentil protein isolate. This produced smaller protein fragments known as polypeptides. The researchers varied the enzyme-to-substrate ratio and treatment time to examine how processing affected the resulting material’s functional properties.

The experiments covered enzyme-to-substrate ratios from 1:100 to 1:2000 and hydrolysis times from two to 240 minutes. A preparation designated LPP5-10, containing partially hydrolyzed proteins below 50kDa, provided a useful combination of solubility, oil-holding capacity and surface properties.

Its oil-holding capacity reached 752%, compared with 174% for the unmodified lentil protein isolate, an increase of more than fourfold. That measurement describes the material’s ability to retain oil, rather than its own fat content or the amount of fat present in the finished yogurt.

The modified protein also had properties that could help stabilize mixtures of oil and water. Its measured surface hydrophobicity was comparable to that of lecithin, an established food emulsifier, while it remained highly soluble across the tested pH range of two to 12. These characteristics helped distinguish the selected preparation from the untreated protein.

For the yogurt experiments, the researchers added 0.05% LPP5-10 to nonfat milk. Yogurt produced from that milk formed a stronger, more structured gel, with mechanical properties that Zhang said were similar to those of yogurt made with whole milk.

“We can take plant protein, chop it into the right-sized pieces and make those pieces behave like a fat-texturizing ingredient,” she said.

The study reported improvements in storage modulus and yield stress. These measurements describe aspects of a gel’s elastic behavior and its resistance to starting to flow, providing a way to assess how the ingredient changed the yogurt’s structure under applied force.

The low inclusion rate is a notable part of the result. The lentil ingredient was used as a texturizer within a dairy formulation, rather than as the main protein source or as a replacement for milk. The experimental product therefore remained dairy yogurt, despite using a plant-derived ingredient to compensate for some of the effects of removing milk fat.

The comparison with whole-milk yogurt concerned physical performance. It should not be read as evidence that the products were indistinguishable in taste, or that the modified protein supplied the nutritional characteristics of the fat it was helping to replace. Zhang explicitly separated those functions when describing the findings.

“Importantly, this study doesn't mean the lentil protein chemically becomes fat or provides the same nutritional properties as fat. It means the modified protein can mimic some of fat's physical and textural functions in food.”

The paper, A plant protein-based fat texturizer: Enzymatic bioproduction and application in non-fat yogurt, was authored by Ishita Ghosh, Federico Harte and Zhang. Ghosh, the first author, earned a doctorate in food science, while Harte is a professor of food science at Penn State. The research received support from the US Department of Agriculture’s National Institute of Food and Agriculture and Hatch Appropriations.

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