ORIGINAL ARTICLE: Effect of rendering on protein and fat quality of animal by-products

Abstract

This work studies the effect of rendering on quality of meat and bone meals (MBM) processed in two Spanish rendering plants according to the standard procedure recommended by 96/499/EC Directive for MBM category III. Twelve samples of raw animal by-products and their corresponding meals were analysed for chemical composition, amino acids (AA) content, FDNB-reactive lysine content, pepsin digestibility, protein dispersibility index (PDI) and fatty acids (FA) content. There was a high variation in MBM composition between and within plants, mainly in the ash and fat content. Rendering caused a decrease in the total (p < 0.05) and the essential (p < 0.01) AA content (in crude protein basis) in both plants, because of a decrease in lysine (p < 0.001), methionine (p < 0.05), threonine (p < 0.01), leucine (p < 0.01), valine (p < 0.01) and phenylalanine (p < 0.01). Besides, there was a reduction in the cystine (p < 0.001), serine (p < 0.01) and aspartic acid (p < 0.01) content. The FDNB-reactive lysine to total lysine ratio and pepsin digestibility only decreased (p < 0.001) in the plant with more severe treatment conditions, whereas the PDI increased (p < 0.05) by the process in both plants. The saturated to unsaturated FA ratio increase on average from 0.73 to 0.88 after rendering, because of the decrease in both linoleic and linolenic acids content and the increase in palmitic and stearic acids content. The results indicate that rendering has negative effects on protein and fat quality of MBM. Variability between and within plants is attributed to differences in raw material, processing conditions and fat removing efficiency. Therefore, a continuous monitoring is recommended to assure the quality of each batch before use.

Valorization of Proteins from Co- and By-Products from the Fish and Meat Industry

“…However, especially the meat and bone meal may be subjected to large variations in nutritional quality. This is mainly caused by variations in composition of raw material and the harsh rendering temperatures [70][71]. In addition, raw materials rich in bone will result in a meal with high ash content, which is associated with low protein digestibility.…”

“…Protein hydrolysates of both animal and fish origin are also increasingly utilized for pet food applications. The hydrolysates contain short peptides and free amino acids that might act as feeding stimulants and palatability enhancers [71,83]. Moreover, protein hydrolysates might have hypoallergenic [84] and bioactive properties (discussed below), which makes it an interesting pet food ingredient for companion animals with special needs.…”

Influence of Process Parameters and Raw Material on the Characteristics of Hydrolyzed Feather Meal

“…It is believed that this reduction is related to the temperature increase of the digester, which is directly proportional to the pressure used in the process. According to Pérez-Calvo et al (2010), the rendering process can affect the protein quality of meat and bone meals [18]. The excessive rendering of feathers leads to a decrease of PC and DV in the hydrolyzed feather meal.…”

“…Eyng et al (2012) stated that the availability of amino acids can be influenced by several factors, including the pressure used in the processing of feather meal [12]. Pérez-Calvo et al (2010) also attributes the variability in protein levels of feather meal to different process conditions, for example, the pressure used [18].…”

In Vitro Methods of Assessing Protein Quality for Poultry

“…Since the 1980s, the PDI method has become a routine technique used worldwide by researchers [17,20,[22][23][24] to assess the quality of protein sources used in monogastric animal feeds. While chemical methods provide an overview of the protein quality of feed ingredients, they do not give a good indication of how much of the nutrient will be absorbed by the animal.…”