In this study, energy and exergy analyses of the closed‐cycle infrared (IR) convective walnut drying were performed. The effects of the combined heat transfer, product–source distance, and temperature–relative humidity (RH) control on the food quality of walnuts and performance were investigated. Experiments were conducted with and without an IR lamp. The temperature and RH of the drying air were set at 40°C and 20%, respectively. The distance between the product and the IR source was changed to 20 cm and 30 cm. The coefficient of performance values of the whole system changed between 1.56 and 2.34. Exergy efficiencies varied between 60.81% and 88.19% without IR and 72.73%–78.54% with IR. Energy and time savings increased by 14.7% and 26.1%, respectively, with using IR at a 20 cm distance compared with the convective system. The fatty acid composition of walnut samples and chemical properties of walnut samples such as total phenolic content, oil, ash, color, antioxidant activity, peroxide values, free fatty acid, conjugated trienes, conjugated dienes, saponification value, and iodine number parameters were analyzed. Food analysis results of all dried walnuts were in the acceptable range. As a result, energy and time savings were achieved with the desired food quality. Novelty impact statement This application makes it possible to achieve the desired conditions with less energy. In this study, the effects of heat transfer mechanisms, the effect of using two mechanisms together, and the effects of the variables within each mechanism on the drying of walnuts were investigated. It has been observed that the addition of an infrared heat source with the right and suitable application shortens the drying time as well as saves energy. As a result of the food quality analysis, it was determined that all products dried without deteriorating the food quality. The closed‐cycle intermittent infrared convective drying system is recommended for industrial use.

Conjugated linoleic acid (CLA) and CLA isomers, present naturally in dairy and meat products, are the natural and functional components. Ruminal microorganisms, such as Butyrivibrio fibrosolvens, lactic acid bacteria (LAB), and propionibacteria can convert linoleic acid (LA) to CLA. In this study, the effect of different linoleic acid (LA) concentrations (0, 0.5, 1, 2%) and different storage time (0, 2, 7, 14 and 21 days) on the CLA content of kefir was investigated. The highest CLA content was found on day 0 in the kefir sample to which 0.5% LA was added but there is no significant difference between control and 0.5% LA. On the contrary, the lowest CLA content belonged to the sample including 2% LA after 21 days of storage. The results suggested that certain amounts of LA could be used to enhance the functional properties of kefir.