The effect of microbial and plant extract preservatives on the chemical, microbial and sensory quality of a traditional fresh South African sausage

Abstract

Boerewors is a traditional fresh South African sausage, made from beef and pork, with a variety of herbs and spices added for flavour. Currently, SO2 is still the main preservative used in Boerewors, with a maximum inclusion level of 450 mg/kg. However, it has come to light that SO2 causes adverse reactions in some consumers; it is severely irritating to the mucous membranes and respiratory tract. As consumers have become more aware of what they eat, there has been an increased demand for minimally processed food products that contain natural ingredients.

In this study, Boerewors was used to evaluate the chemical, microbial and sensory efficacy of natural preservatives that could potentially replace SO2. The six Boerewors treatments were formulated according to the recommended inclusion levels of each preservative. To replicate retail conditions, the Boerewors was stored at 4 °C for 6 days for most of the analyses and stored at -18 °C for lipid oxidation stability analysis. The effects of no preservatives, microbial preservatives, plant extract preservatives, and SO2 as preservative, were evaluated. Water activity, pH and moisture content were inconsistently influenced. However, the lipid oxidative stability results were encouraging, as the effects of the plant extract preservatives surpassed that of SO2. The microbial results were inconclusive, due to the protective culture treatments containing viable microorganisms. The colour of the Boerewors remained quite stable, but SO2 maintained the red colour of Boerewors the best. In the consumer sensory evaluation, it was established that there was not a preference for a specific treatment.

The Boerewors was sampled on the first day and evaluated by profiling the microorganisms on a community level. The results showed that the treatment with no preservatives added had the largest and most diverse microbial community, while the microbial community in KD1 was the smallest and least diverse and was functionally more similar to the SO2 treatment than the other treatments. The Gompertz based results showed that the microbial community in PrC1 started to grow at a much later stage than the other treatments, and KD2 had the least explosive growth of the treatments.

The protective cultures were excluded from the spiking experiment and the efficacy of four treatments, on the microbial safety of the Boerewors, inoculated with either E. coli or S. aureus, were monitored. The treatments affected the growth and survival of E. coli, as the results showed that plant extracts maintained the product safety similar to that of the SO2 140 Boerewors treatment. The SO2 Boerewors inhibited the growth of S. aureus the most but adding the plant extracts proved to be better than adding no preservative. Survival rates of both inoculated strains decreased from day 0 to 6, while it was stored at 4° C.

Overall, the results of this study showed that replacing SO2 with natural preservatives, specifically plant extract preservatives, KD1 and KD2, maintained the chemical, microbial, and sensory quality, and product safety as efficient as SO2. Thus, it is recommended that the meat industry consider including natural plant preservatives when reformulating Boerewors.

The preliminary cost estimates for inclusion of the natural plant extracts as replacers of SO2 in Boerewors indicated that it will be financially viable.