P.PSH.1430 - Reduction of Vitamin A in lamb liver for pet food application

Summary

Liver is a highly palatable and nutrient-dense organ used as an ingredient in pet food formulations, and abundantly produced by the meat industry. However, liver can only be included into pet foods in limited quantities owing to its high vitamin A (VA) content to prevent toxicity in cats and dogs. Currently, pet food manufacturers do not know the VA content of their liver ingredients as it varies with the age and diet of the animal, and different regional sources of liver may vary substantially. As a result, manufacturers must maintain a relatively low inclusion rate (generally recommended to be <5-10 wt% DM of the diet) to ensure the consumption of the final product will not lead to VA toxicity.

To enhance the overall palatability and nutritive value of pet food and treats, it would be advantageous to include liver in higher proportions, without concomitant increase in total VA in the final formulation.

The project findings will be primarily of use to the red meat and pet food industry, specifically red meat processors, and ingredient and pet food manufacturers, to determine whether such a process warrants further investigation.

Objectives

This project set out to determine whether simple non-polar liquid extraction of vitamin A from liver using hexane, vegetable oil or tallow is technically feasible.

Key findings

All the tested solvents reduced the vitamin A content in both fresh and dehydrated liver. On a dry matter basis, 45-64% reduction in vitamin A was observed for fresh liver, and 68-91% reduction for dehydrated liver. These results reflect our provisional extraction conditions, relating to liver-to-solvent ratios, temperature, time, agitation and separation method. At this point it is not possible to identify the conditions that optimise efficiency and consistency, or that might apply to scaled-up processes.

The oily solvents were not completed separated post-extraction and some remained in the liver residue. This increases processing variability (particularly between solvents) and confounds calculations of true yield. In terms of mass, the results were:
- A post-extraction liver product prepared from fresh liver contained 267–409 mg/kg DM vitamin A (initially 741 mg/kg DM vitamin A).
- A post-extraction liver product prepared from dehydrated liver contained 43–163 mg/kg DM vitamin A (initially 502 mg/kg DM vitamin A).

Benefits to industry

The experimental results show that vitamin A can be extracted from fresh or dehydrated liver using animal or vegetable lipids, and centrifuged post-extraction to produce a proteinaceous liver fraction with at least 45-68% less vitamin A (on a dry matter basis) and a recovered lipid fraction containing 1.8–23 mg/L vitamin A. The wide range is a consequence of the solvents and conditions used in this proof-of-concept project, as well as the initial liver vitamin A concentrations that varied by up to two-fold.

Current maximum levels for vitamin A in dog and cat food formulations are 75 and 99 mg/kg DM respectively, and this has limited the usefulness of liver as an ingredient. Based on the average results observed here in this proof of concept, and if similar reductions can be obtained through a commercial scale process, pet food formulations might be able to contain a post-extraction liver ingredient at quite high inclusion levels, assuming no other ingredients are contributing to vitamin A in the food formulation.

Based on the project results:
A post-extraction liver product prepared from fresh liver could be incorporated in pet food formulations at 18-28% DM for dogs, and 24-37% DM for cats, before exceeding the maximum allowable value for vitamin A.

A post-extraction liver product prepared from dehydrated liver could be incorporated in pet food formulations of at least 46% DM for dogs, and at least 61% DM for cats, before exceeding the maximum allowable value for vitamin A.

Future research

Further research could optimise liver preparation and extraction conditions, assess the quality and safety of the produced materials and refine the business case for the technique. This may include:
- Optimisation of the time-temperature treatment and agitation method for an appropriate set of edible oils to be used as non-polar solvents.
- Establishment of a consistent extraction process that delivers known upper values of vitamin A in the final product irrespective of starting concentrations in the raw material, which may require a polishing stage to achieve.
- Assessment of the quality and techno-functional properties of the liver protein fraction (e.g. gel strength, water/oil retention capacity and level of protein denaturation) and lipid fraction (e.g. peroxide value).
- Determination of recovery and extraction efficacy through pilot-scale trials.
- Technoeconomic assessment to determine the viability of an industrial process at a range of commercial production capacities.
- Assessment of protein and lipid digestibility, or other health benefits of the products for specific applications.
- Characterisation of the nutritional profile of the recovered liver protein and lipid fractions
Assessment of the palatability of both the liver protein and lipid fractions.