Retorting conditions affect palatability and physical characteristics of canned cat food

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Moist commercial feline foods are manufactured using retort processing to sterilise and preserve the product and to obtain a desired consistency. During retorting, food contents are sealed in airtight cans, containers or flexible pouches and are subsequently heat treated⁽¹⁾. The effectiveness of a heating process in achieving product sterility can be evaluated by determination of the lethality value (F ₀) of the process. The F ₀ represents the time equivalent of a heating process to destroy micro-organisms at the reference temperature of 121·1°C and serves as a standard to compare sterilisation values for different processes⁽²⁾. Any process which achieves an F ₀ of 3 min is considered to render the product free from pathogenic organisms, which could create a public health danger⁽³⁾. In pet food production, however, higher values (F ₀ values > 10) are employed in order to destroy bacterial spores as well⁽²⁾. Besides sterility of a product, additional factors related to the product quality such as physicochemical factors and palatability may be affected by the retorting conditions.

Little is published in the scientific domain on effects of retorting conditions on physicochemical factors of canned pet food. Niamnuy & Devahastin⁽⁴⁾stated that excessive heating temperature and time may lead to overcooking and lead to undesirable textural characteristics of a product, as this may affect the binding properties of the product. As texture is in close relationship with palatability (as chewiness, hardness and elasticity affect mouth feel of the product), excessive heating may also negatively affect palatability. With regard to palatability, under high temperature and pressure of retorting, desirable flavour compounds, like sulphur-containing thiazole and thiopene compounds, can develop as a result of occurrence of the Maillard reaction between free reactive amino groups of specific amino acids and reducing sugars⁽⁵⁾. On the other hand, Heinicke⁽⁶⁾reported that an increasing retorting time may negatively influence palatability for cats, which may be attributed to formation of lipid peroxides, and/or more aroma-intensive heterocyclic Maillard reaction products, such as pyrrole, pyridine and pyrazine, giving undesirable flavours during retorting⁽⁴