Optimizing Sourdough Processing for the Production of ɣ-nonalactone (Fruity Aroma) by Lactobacillus sanfranciscensis Using Headspace Solid-Phase Microextraction Method

Background and Objectives: Sourdough processing is a well-known method to improve food flavor. One of the most important lactic acid bacteria isolated from sourdoughs is Lactobacillus sanfranciscensis. Because of the bacterial ability for acidification and liberation of the volatile compound precursors, it can strongly affect dough rheology and aromatic properties. In this study, the best conditions for production of ɣ-nonalactone (with fruity aroma) in sourdough were investigated for the first time.  Materials & Methods: To prepare sourdough, a mixture of rye and barley flour and wheat bran was used. Fermentation was carried out using Lactobacillus sanfranciscensis ATCC 4332. Experiments were designed using response surface methodology and five factors, including time, temperature, dough yield and sorbitol and bran proportions. Volatiles were extracted from sourdough using headspace solid-phase microextraction method. Extracted volatile compounds were measured using gas chromatograph coupled with a mass selective detector. Results: Effects of independent variables on ɣ-nonalactone production were modeled using central composite design. Experimental data were similar to the predicted data; therefore, results of this model were reliable. Based on the results, fermentation at 37 ºC for 72 h with DY of 400, sorbitol of 6% and 20% of bran provided the most optimum conditions for the production of fruity aroma (26.3 ppm). Conclusion: Investigation of the aromatic profile of sourdough fermented by L. sanfranciscensis showed that this strain was capable of producing desirable aroma during fermentation. Based on the results, time and temperature included strong effects on production of ɣ-nonalactone. In comparison, dough yield did not include significant effects while addition of bran and sorbitol included mild effects.