Wheat germ stabilisation: heat treatment or sourdough fermentation? An industrial case

Wheat germ is strongly susceptible to oxidation, being characterized by a high content of unsaturated oil (Sjövall et al., 2000). In order to be used in various food products, wheat germ is conventionally stabilized by heat treatments (Sudha et al., 2007), even if they often cause a decrease in the nutritional value of germ. This work was aimed at investigating the suitability of sourdough fermentation for stabilizing germ from common wheat (Triticum aestivum sp.) on industrial scale. For this purpose, the raw germ (WG) was fermented with a sourdough and dried at low temperature (WGF). WGF was compared to wheat germ stabilized by using the heat treatment commonly applied on industrial scale (60s @120°C) (WGH). All the treatments were carried out in collaboration with Molino Quaglia S.p.A. Physico-chemical characteristics (aw, pH and TTA), enzymatic activities (alpha-amylase, lipase and lipoxygenase), development of rancidity (headspace analysis) during storage (90 days @ 25°C) of wheat germ samples, and rheological properties of germ-enriched dough by MVAG, Farinograph, and Rheofermentometer were evaluated. Sourdough fermentation seemed not to affect the pH (6.8±0.01 for WG, 6.7±0.13 for WGF), and consequently the TTA (14.1±3.4 for WG, 17.5±0.7 for WGF), of wheat germ, probably due to the industrial conditions used for fermentation. Nevertheless, sourdough fermentation on industrial scale was effective for decreasing the enzymatic activity of wheat germ. Indeed, in the case of WGF the lipase activity was 2.6-fold lower than that found in WG, according to Rizzello et al. (2010), and about 1.5-fold lower than that found in WGH. With regard to the hexanal in headspace during wheat germ storage, both WGH and WGF samples showed a strong decrease in its concentration (4÷7-fold lower than that found in WG), confirming the good stabilization action of sourdough fermentation. Furthermore, the sourdough fermentation seems to have a similar effect on rheological properties of enriched dough as the conventional heat treatment. In conclusion, the industrial sourdough fermentation followed by low temperature drying could be considered as a useful process for making a stabilized product better than that one obtained with conventional heat treatment.