Studies On Preparation Of Lactic Acid Sourdough Starters And Their Fermentation And Baking Properties

The freeze-drying of various starters fermented with L. plantarum (LP) or L. sanfranscensis (LS) and produced with all purpose flour or whole wheat flour, and their effects on rheological and biochemical properties of corresponding doughs, and the influence of sourdough fermentation on baking characteristics and bread flavor were studied in this paper.The four lactic acid bacteria (LAB) sourdough starters were named PA (LP starter produced with all purpose flour), SA (LS starter produced with all purpose flour), PW (LP starter produced with whole wheat flour), and SW (LS starter produced with whole wheat flour). LAB fermentation could shorten the fermentation time and save cost. Total titratable acidity of whole wheat starters (WWS) were higher than that of all purpose flour starters (APS). Trehalose was protective on LAB in freeze-dried LAB sourdough starters. The addition of trehalose to APS enhanced the acidification capacity of LAB in starters, with the highest survival rate at the level of 10%. Significant influence of trehalose was detected on acidification capacity of LAB in WWS, with the strongest acidification capacity and highest survival rate at the level of 15%.Mixolab, dynamic rheometer and rheofermentometer were used to analyze the effects of LAB sourdough starters on the thermomechanical, dynamic rheological and rheofermented properties of corresponding doughs. The addition of starters decreased the dough development time (from 7.05 min to 5.53 min for PA and to 5.08 min for SA in common doughs; from 10.72 min to 10.22 for PW and to 9.56 for SW in whole wheat doughs, same below), water absorption (from 63.1% to 61.9% and 61.3% in common doughs, and from 65.3% to 64.6% and 63.8% in whole wheat doughs) and stability (from 11.30 min to 10.09 and 9.93 min in common doughs, from 10.70 min to 8.52 and 9.45min in whole wheat doughs), aggravated dough weakening but maintained viscoelasticity, promoted dough expansion height (Hm, from 45.0 mm to 53.1 and 51.7 mm in common doughs, from 43.6 mm to 49.1 and 50.2 mm in whole wheat doughs) and gas holding capacity, accelerated starch gelatinization rate, inhibited staling, and improved cooking stability. Chemically acidification destroyed dough stability and viscoelasticity, and decreased dough expansion height, fermentation tolerance and gas holding capacity. Whole wheat doughs had higher water absorption and faster enzymatic degradation rate than common bread doughs, whereas with longer development time and lower stability. PA (LP starter produced with all purpose flour) was shown to prefer improving rheofermented properties of common bread dough; elsewise SW (LS starter produced with whole wheat flour) could significantly increased the viscoelasticity of whole wheat dough.Organic acids content and total free amino acid content during fermentation were determined using HPLC to analyze the effects of LAB sourdough starters on the biochemical properties of corresponding doughs. The contents of fermentation products, including lactic and acetic acids, and amino acids, were related to fermentation substrate and microbial strain. There were significant differences among TTA values of four starters, with WWS (9.31 mL of PW and 11.33 mL of SW) higher than APS (4.49 mL of PA and 4.96 mL of SA) and LS starters higher than LP starters. Lactic and acetic acids contents were decided by fermentation type. Homofermentative LP produced more lactic acid (9.8387 g/g dry sample of PA and 13.4249 g/g dry sample of PW), however, heterofermentative LS produced more acetic acid (0.4092 g/g dry sample of SA and 0.5637 g/g dry sample of SW). Higher amount of organic and free amino acids (63.7830 mg/100g dry sample of PW and 66.3295 mg/100g dry sample of SW) with higher TTA values were obtained in whole wheat system because of the relatively more existence of fermentable sugars. During to the dilution of flours and other ingredients, the acidity and fermentation product contents of mixed doughs decreased. After proofing, the acidity and total free amino acid content increased, and lactic and acetic acids contents increased with strain-specialty. Whole wheat was favorable to produce fermentation products, with higher contents of sourdoughs than non-sourdoughs.Effects of LAB sourdough starters on baking characteristics and bread flavor were analyzed through the determination of specific volume, hardness, moisture migration, amylopectin retrogradation enthalpy change, and volatile compounds of corresponding breads. The addition of starters could improve bread specific volume and texture, inhibit moisture migration and amylopectin retrogradation, and polish up baking characteristics and bread flavor. Total volatile contents of breads containing LS starters were higher than those with LP starters. Whole wheat breads contained more volatiles with several compounds of importance such as 3-methyl-1-butanol, 3-hydroxy-2-butanone, furfural, 3-methyl-buatnoic acid and benzeneethanol, which endued whole wheat breads with more fragrant malty, milk-like, almond, fresh and sweet flavor. Some lactones, for instance 5-butyldihydro-2(3H)-furanone, were promoted to generate by PA and SA (LS starter produced with all purpose flour), therefore common sourdough breads had more coconut-like and fruity flavor. Chemically acidification resulted in degradation of baking quality and bread flavor.