Oat Okara – Characterization and Potential Product

Abstract

There is an increasing demand for plant-based foods and a growing interest in valorising by-products from food production. One such plant-based by-product is oat okara, the fibre- and protein-rich residue generated during oat drink production. Due to its high moisture content and associated microbial instability, oat okara is currently underutilized and is primarily used as animal feed or discarded. The aim of this master's thesis was therefore to character-ize oat okara as a food raw material, evaluate the effects of heat treatment on its microbial and functional properties, and investigate its application in a tortilla prototype.

The oat okara was characterized with respect to nutritional composition, thermal behaviour, rheological properties, microbial status, water- and oil-holding capacity, and colour. Rapid Visco Analysis (RVA) and Differential Scanning Calorimetry (DSC) were used to study physicochemical changes during heat treatment. Heat treatments at 140℃ and 100℃ were evaluated for microbial reduction and their influence on functional properties. In addition, tortillas containing oat okara were produced and compared with commercial fibre-rich tortil-las regarding texture, water activity, colour, and thermal properties.

The results showed that oat okara contained high levels of protein and water. RVA and DSC analyses indicated that heat treatment affected both protein denaturation and fibre function-ality, likely through conversion of insoluble fibres into soluble fibres at elevated tempera-tures. Heat treatment improved water- and oil-holding capacity and reduced microbial counts to acceptable levels for bakery applications, although complete microbial inactivation was not achieved at 100℃. The tortilla prototype exhibited high protein and fibre content but showed lower stretchability and higher water activity than commercial references, indicating challenges related to texture and shelf stability.

Overall, the results demonstrate that oat okara has strong potential for use in sustainable food applications, although further optimization of heat treatment and product formulation is re-quired to improve safety, texture, and storage stability.

Popular Abstract

Oat drink is becoming more and more popular, both as an alternative to milk for vegans or lactose intolerant people, and as a good tasting drink in of itself. While the production of oat drink increases, the waste created increase as well, resulting in large amounts of potential food being thrown away or turned into animal feed. This potential food source is called oat okara, named after okara, the similar waste product created during soy drink production. It is a fibre and protein rich material that taste pleasantly of oats, so why are we throwing it away?

The main reason is that oat okara is wet and hot when it comes straight from the oat drink production, a perfect breeding ground for bacteria and moulds. It also contains bacteria spores, bacteria that have created a protective shell around itself to survive in conditions where other bacteria die, for example during cooking. If the finished food made with oat okara is then heated at lower temperatures for a longer time, let’s say you let a pie sit in the still hot oven until your gests arrive for a dinner party, the spores can start growing again and potentially cause food poisoning. To prevent this, the oat okara used here was frozen imme-diately after collecting and heated at a higher temperature to try and kill both the bacteria and their spores. After 1 minutes at 140℃, next to all bacteria and spores were killed, mak-ing the oat okara safe to eat.

Oat okara was heat-treated at different temperatures beside 140℃, mainly at 100℃ for 6 minutes, but also 120℃. When heat-treating oat okara at 120℃, an unexpected phenomenon was found. To understand it, the concept of viscosity needs to be explained. Viscosity is how easy a fluid flow, the higher viscosity the slower it behaves. For example, water has a lower viscosity while a thick sauce has a higher viscosity. A material can change its viscosity when the temperature rise because of internal reactions to the heat. With a viscosity meter, these changes can be measured. In the untreated oat okara, the viscosity increased once when a protein changed form because of the heat. After heating the oat okara to 140℃ and holding it there for 4 minutes, the viscosity did not increase because of the protein anymore, that had already happened during the heat-treatment, but the viscosity did increase. The theory is that it was the fibres in the oat okara that caused the viscosity increase. Normally the fibre in oat okara is insoluble and do not cause an increase in viscosity, but because of the heat-treatment, some insoluble fibre could have been broken down to soluble fibre that do in-crease viscosity when heated. The oat okara that was heat-treated at 100℃ for 6 minutes had viscosity increases both from the theorised fibre transformation and from the protein, putting it between the untreated oat okara and the oat okara heat-treated at 120℃.

The heat-treated oat okara was used to make tortillas, replacing some of the wheat flour in tortilla bread batter. It resulted in thicker tortillas that wasn’t as stretchable as high fibre tor-tillas you can buy in the store, but they have a lot of potential. With some time to perfect the making of oat okara tortillas, as well as the heat-treatment so that spores are killed as effec-tively at 100℃ as at 140℃, they can become a great prototype for how oat okara can be used as a food ingredient, decreasing food waste and making use of the food grown here in Sweden.

• author: Johansson, Ylva
• supervisor: Jeanette Purhagen; Abhinav Majumdar
• organization: Food Technology and Nutrition (M.Sc.)
• course: KLTM06 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Agriculture and Food Sciences
• keywords: oat okara, bacteria spores, heat-treatment tortilla, food engineering nutrition and food chemistry
• language: English
• id: 9246714
• date added to LUP: 2026-08-10 09:50:23
• date last changed: 2026-08-10 09:50:23