Plant-based alternatives to traditional meat sausages are increasingly important in the food industry. The changing consumer habits for ethical and/or health reasons have led to a drive by food producers to develop tasty, plant-based sausage products.
Fat oxidation leads to off-flavors
The difficulty in producing a successful plant-based sausage alternative is not limited to its taste and appearance. Because these plant-based alternatives behave differently to conventional sausage products, their sensory, chemical, and microbiological changes during storage (equating to shelf-life) must be extensively studied. Whereas the microbial stability of conventional sausage products is ensured by specific measures, such as longer curing processes and/or the use of curing salt or smoking, plant-based products are often boiled to inhibit microbial growth.
Besides containing alternative proteins, plant-based sausage products contain large amounts of fats (e.g. sunflower oil or rapeseed oil) and are therefore prone to oxygen-driven spoilage in the form of fat oxidation. The high susceptibility of plant fats to oxidation leads to the development off-odors and off-flavors in these plant-based alternatives.
Our studies on the oxygen sensitivity of plant-based sausage and meat alternatives
The objective of this project was to identify spoilage indicators in plant-based sausage and meat alternatives; in particular, we assessed the sensory changes and analyzed the fat oxidation products in relation to oxygen scavenging.
Key aspects of the project were:
- Identification of suitable raw materials
- Evaluation of the effect of the oils/fats in the products
- Evaluation of oxidation markers and color changes
- Correlation between sensory and analytical data
Studies were carried out on two self-produced mycoprotein-based products containing either rapeseed oil or sunflower oil. The products were refrigerated (at 6°C) and stored under protective atmospheres comprising 0%, 2%, or 20% oxygen in nitrogen. Samples were tested over a storage period of 4 weeks.
In addition to common oxidation markers, such as pentanal and hexanal, other fat oxidation products that contributed to off-odors were detected, including (Z)-4-heptenal, (E,E)-2,4-nonadienal, and (E,E-2,4)-decadienal. Analyses revealed that the concentrations of these compounds increased exponentially with storage time. The product containing sunflower oil exhibited particularly high quantities of these oxidation products due to the presence of greater amounts of polyunsaturated fatty acids. An observed color change during storage was related to alterations in the coloring agents in the product, which are sensitive to oxygen and light.
The right packaging
Our investigations demonstrated that use of modified atmosphere with minimal oxygen slows the oxidation processes. While products can be protected against oxidation by packaging them under a protective atmosphere comprising carbon dioxide and nitrogen, technical issues mean that up to 2 %vol. oxygen can remain in the packaging. Our studies showed that even this small amount of oxygen can promote oxidative changes in these products.
Even at a modified atmosphere oxygen concentration of only 2%, the oxidation markers hexanal and pentanal were detected within 4 weeks of storage, as were the associated sensory changes. However, the use of oxygen scavengers was found to lower the oxygen concentration to almost 0%, which suppressed oxidation and prevented an increase in hexanal and pentanal concentrations during storage.
Improved quality stability
In summary, the project demonstrated that the fatty acid composition of the oils has a significant influence on the quality of the product. The oxygen scavenging was found to correlate with the color changes, the formation of fat oxidation products, and the sensory changes. The use of scavengers reduced the oxidation and prolonged the shelf-life of the products in terms of chemical and sensory changes. Further projects will study the microbial changes (both qualitatively and quantitatively) in greater detail, which is important because new products such as these involves the use of 'new storage atmospheres', namely oxygen-free storage, which could promote the formation and/or propagation of anaerobic microorganisms (spore formers).