Effect of enzymatic pretreatment on yield and quality of animal fats obtained by low-temperature rendering

The growing demand for sustainable utilisation of animal by-products has increased interest in technologies that improve fat recovery while preserving the nutritional and physicochemical quality of rendered fats. The growing interest in the sustainable utilisation of animal by-products is associated with the need to reduce waste generated by the meat industry, improve resource efficiency and implement circular-economy strategies in food production. This study evaluated the effect of enzymatic pre-treatment with papain and bromelain on the efficiency of low-temperature vacuum rendering of pork and beef subcutaneous adipose tissues. Adipose tissues were incubated with papain (30 and 50 mg kg⁻¹) or bromelain (30 mg kg⁻¹) prior to rendering at 95±2°C under reduced pressure (200 mbar). The rendered fats were evaluated for rendering yield, fat-to-crackling ratio, physicochemical quality (acid, saponification, iodine and peroxide values), instrumental colour (CIELAB) and fatty acid composition. Enzymatic pre-treatment significantly improved rendering efficiency (p < 0.05). The highest rendering yield (66.85%) and fat-to-crackling ratio (2.91) were obtained for beef adipose tissue treated with 30 mg kg⁻¹ papain, whereas untreated pork adipose tissue showed the lowest values (57.98% and 1.95, respectively). Despite these improvements, acid and peroxide values remained low in all treatments, indicating limited hydrolytic and oxidative deterioration under low-temperature vacuum rendering conditions. Bromelain treatment produced the greatest changes in colour, significantly increasing yellowness (b*), chroma and hue angle, while papain preserved the colour characteristics of beef fat close to those of the untreated control. Fatty acid composition was determined primarily by animal species rather than enzymatic treatment. Beef-derived fats contained significantly higher proportions of saturated fatty acids, stearic acid, vaccenic acid and conjugated linoleic acid (CLA), whereas pork-derived fats were characterised by higher levels of oleic acid and polyunsaturated fatty acids. Enzymatic pre-treatment did not substantially alter the nutritional fatty acid profile of the rendered fats. These findings demonstrate that proteolytic pre-treatment, particularly with papain, is an effective strategy for increasing fat recovery during low-temperature vacuum rendering while maintaining the physicochemical quality, oxidative stability and characteristic fatty acid composition of rendered animal fats. The proposed approach offers considerable potential for industrial production of high-quality edible rendered fats with improved process efficiency.