Size and shape attributes of packaging remnants in former food products

Former food products (FFPs) are alternative feed ingredients used in livestock diets. They are surplus rejected by human market but do not post microbiological nor hygienic risks when considered as feedstuffs. However, even the processes of transforming FFPs into animal feed often include mechanical unpacking and grounding, the final products may be still prone to packaging contamination. Common materials of packaging remnants in FFPs are aluminum, cellulose, and plastic. Therefore, it is important to investigate and to provide information regarding the size and shape attributes of these materials so as to improve the processing techniques in feed industry. A total of 441 packaging remnants from 17 sources of FFPs were included in this study. The Fourier transform infrared spectroscopy coupled with an optical microscope was used to identify the material of the packaging remnants, which resulted in a categorization of remnants consisting of 44 aluminum, 308 cellulose, and 89 plastics. The categorized remnants were observed with a stereomicroscope and were subsequently measured by a digital camera and an image analysis software. Each measurement contains 21 size descriptors and 9 shape descriptors in which some of them were derived from calculations. The values obtained were standardized for plotting and statistical analysis. The principal component analysis suggested that one size descriptor, area, explained 84% of the total variability in the size of remnants. Additionally, aluminum remnants tended to have smaller areas compared to cellulose and plastic ones. The distribution of values for shape descriptors overlapped between the three materials. However, aluminum remnants showed a narrower range in descriptors such as roundness and solidity than remnants composed by the other two materials. Through the information provided by the image analysis and the measurements, it was concluded that the obtained values in terms of size and shape attributes distributed broadly rather than following a specific pattern. Nevertheless, the measured values of aluminum remnants seemed to be more consistent compared to the ones of cellulose and plastic remnants. Namely, aluminum remnants tended to be smaller in size and have narrower distribution in shapes. This could be associated with the intrinsic property of aluminum used in food packaging and the processing protocols run in the feed plant. The most common form of aluminum in FFP packaging is aluminum foil which is very thin and malleable. After several mechanical processing, aluminum remnants could be folded and become more compact, which contributes to their smaller sizes and more regular shapes. Overall, this study aimed at providing information about size and shape attributes of packaging remnants in three different materials. To distinguish between aluminum, cellulose, and plastic remnants, other properties of the materials have to be considered.