مدل‌سازي قوام خميرترش و ارزيابي تاثير آن بر ويژگي هاي نان حاصل از آردهاي ايراني به عنوان تابعي از شرايط تخمير كشت آغازگر اختصاصي

Modeling of sourdough consistency and evaluation of its effect on iranian breads properties as a function of specific starter culture fermentation conditions

در اين پژوهش، تاثير دماهاي 28 و 32 درجه سانتي‌گراد و زمان‌هاي تخمير 16و 24 ساعت دو نوع كشت آغازگر اختصاصي شامل لاكتوباسيلوس پلانتاروم و نسبت مساوي از مخلوط سويه مذكور با لاكتوباسيلوس برويس بر قوام خميرترش و سپس تاثير اين شرايط تخميري بر pH و اسيديته قابل تيتر خميرترش و همچنين حجم مخصوص پس از پخت، سفتي بافت، عطر و طعم نان‌هاي خميرترشي حاصل از آرد‌ مورد استفاده در تهيه نان‌هاي بربري، تافتون، سنگك و لواش مورد ارزيابي قرار گرفت. قوام اين نمونه‌ها بر اساس روش‌ قوام سنجي آدامز، بررسي و با نمونه شاهد مقايسه شد. اين آزمايش‌‌ها در قالب طرح پايه كاملا تصادفي و با چهار تكرار صورت گرفته و مدل‌هايي به منظور ارزيابي شرايط تخمير كشت‌ آغازگر اختصاصي بر قوام خميرترش حاصل از آردهاي مذكور ارايه گرديد. نتايج حاصل نشان داد كه شرايط تخمير بر قوام خميرترش حاصل از آرد‌هاي مورد استفاده در مقايسه با نمونه شاهد، تاثير معني‌داري دارد (01/0? p). بر اساس اين نتايج، نمونه‌هاي فرآوري شده با آغازگر لاكتوباسيلوس پلانتاروم در مقايسه با آغازگر ديگر و همچنين نمونه‌هاي فرآوري شده با آرد بربري در مقايسه با ساير آردها داراي مقادير گسترش‌پذيري بيشتري بودند. علاوه‌ بر اين، در اكثر اين تيمارها تفاوت معني داري بين مقادير اسيديته قابل تيتر خميرترش هاي حاصل از آردهاي بربري و سنگك با يكديگر و همچنين خميرترش هاي حاصل از آردهاي تافتون و لواش با يكديگر مشاهده نشد. مقادير گسترش پذيري خميرترش-هاي حاصل از آردهاي تافتون و لواش نيز تفاوت معني داري با يكديگر نداشتند اما اين تفاوت بين خميرترش هاي حاصل از آردهاي بربري و سنگك كاملا معني دار بود. بيشترين ميزان حجم مخصوص نيز در نان فرآوري شده با خميرترش داراي لاكتوباسيلوس پلانتاروم در مقادير بيشينه دما و زمان تخمير هنگام استفاده از آرد بربري بدست آمد اما روند تغييرات سفتي بافت، عطر و طعم نان‌هاي خميرترشي از الگوي معيني پيروي نكرد.

Introduction: Sourdough has been used since ancient times and sourdough fermentation has been studied for its effect on the sensory, structural, nutritional and shelf life properties of bread. During fermentation, biochemical changes occur in the carbohydrate and protein components of the flour due to the action of microbial and indigenous enzymes. The rate and extent of these changes greatly influence the properties of the sourdough and ultimately the quality of the final baked product. From a rheological point of view, it is well established that as fermentation progresses, there is a change in nature of the elements contributing to dough structure such as the decrease in the viscosity. During sourdough fermentation, lactic acid bacteria produce a number of metabolites which have been shown to have a positive effect on the texture of bread. In addition to the direct impact of decreasing pH values on dough characteristics, secondary effects of acidification and fermentation time may include changes in the activity of cereal or bacterial enzymes associated with changes in the pH of the environment during the fermentation period. Further to the impact of sourdough on the structure and rheology of the constituent gluten proteins making up the framework of the dough, its effect on gas formation must also be considered in view of the fact that gas formation by microorganisms is necessary in order to obtain leavened bread. The application of sourdough to wheat breads has also a positive impact on bread volume. The rate of application is important, however, because optimum levels of sourdough must be applied to achieve optimal bread quality. The nature of the acidification process may also be a key. The present study was undertaken to evaluate the effects of different fermentation conditions on sourdough consistency and properties of Iranian main breads. Materials and method: In this research the fermentation temperatures (28 and 32 ?C) and fermentation times (16 and 24 hours) effects of two specific starter cultures including Lactobacillus plantarum (ATCC 43332) and a mixture of this starter with Lactobacillus brevis (ATCC 14917) on consistency of sourdoughs produced from flours of Iranian main breads (Barbari, Taftoon, Sangak and lavash), were investigated. An inoculum of mentioned strains was added to the mixture of water and wheat flour. The mixture was allowed to ferment at different fermentation temperatures and times without agitation for sourdough preparation. Then an amount of 0.5% active dry yeast extract, containing Saccharomyces cerevisiae and 25% sourdough samples (w/w) were added to each 100 g flour and mixed. The dough was left for bulk fermentation and at the end of the fermentation time; each piece was rounded before moulded by hand. The moulded dough pieces were proofed for 1.5 h at 30 ± 1 ?C and 85% relative humidity before baking at 220 ± 5 ?C for 15–16 min in a heated oven and then cooled in aseptic conditions for 1 h. The effect of fermentation conditions on pH and total titerable acidity of sourdough and also specific volume (rapeseed displacement method), firmness, aroma and flavour (based on organoleptic analysis) of sourdough breads prepared from the mentioned flours, were evaluated. Sourdoughs consistency were also estimated by Adams consistometer and compared with control samples. In these experiments a completely randomized design with four replications were conducted. Results and Discussion: Based on the results, some models were developed. These results showed that, fermentation conditions had significant effect (p?0.01) on sourdough consistency prepared from flours of main Iranian breads in comparison with control samples. Moreover the produced samples with L. plantarum compared to other starter culture and the samples processed with Barbari flour in comparison with other flours had higher extensibility values. In most treatments, total titerable acidity in Barbari and Sangak sourdoughs and also Taftoon and Lavash sourdoughs were the same. The consistency of Taftoon and Lavash sourdoughs were also similar, but consistency of Barbari and Sangak sourdoughs were completely different. The maximum amount of specific volume was observed in sourdough bread, produced with L. plantarum in highest amounts of fermentation temperature and time and using of Barbari flour, but the changes in firmness, aroma and flavour of sourdough breads did not follow a specific pattern. There exist a myriad of microbial, technological and processing dimensions that must be considered in order to produce cereal products of optimum quality. Significant advances have been made in understanding the contributions made by the presence of acids, the fermentation period and the role played by cereal and bacterial enzymes in terms of sourdough and bread characteristics. Conclusion: process requirements for optimum quality were strain-specific and different for textural improvement which should be taken in to account in designing future sourdough baking processes. Keywords: Specific starter culture, Iranian flours, Dough consistency, Bread specific volume.