Use of dough mechanical properties in the prediction rheology of dough, quality, sensory, shelf life and microstructure of bread: investigation by asymmetric and symmetric multivariate methods

Flat breads are the main dietary staple in many Middle Eastern and North African countries. In today’s demanding world, the use of bread improvers has become an indispensable part of enhancing the quality of bakery products. Bread improvers are technically sophisticated blends of functional ingredients, which if formulated correctly, will enhance the development of dough structure, facilitate trouble-free production, and provide the desired result of consistent products having optimal quality at the lowest possible cost. Among the functional food additives, polyols have been increasingly used to improve the quality and shelf life of bread. Polyols have been used successfully to extend the shelf life of ready to eat bread used by the military, Barbari bread fortified with soy flour, as well as flour tortillas. Emulsifiers, a subset of surfactants, have been widely used by the baking industry. The function of surfactants, as crumb softening agents, is closely related to their interaction or complex formation with starch, particularly the linear amylose fraction, to retard bread staling. Surfactants, such as SSL and DATEM that are the most efficient in breadmaking are able to form lamellar mesophases or gel structures in water. It has been shown that for polar lipids the lamellar liquid-crystalline phase is the most effective form in which this component can be added to bread dough in order to improve loaf volume. Mechanical properties of dough play an important role in baking industries. In a few cases, it can be desirable, for example, to fix some ingredients on bakery products. The dough is expected not to stick to metal surfaces and to show a good resistance to vibration and mechanical shock to minimize detrimental effects such as process breakdown, production loss and contamination of the equipment. Thus, the present study was designed: (a) to examine the effects of different emulsifiers (sodium stearoyl-2-lactylate and diacetyl tartaric acid esters of monoglycerides) and polyol (propylene glycol) on Barbari flat bread performance when used singly and in combination at different levels; (b) to obtain the relationship between mechanical and rheological properties of dough and quality, shelf life, sensory and image parameters of bread using the asymmetric methods (response surface methodology and partial least squares regression) and symmetric methods (coefficients of determination and Principal components analysis) and (c) to determine the optimum formulations for Barbari flat bread improver.
Commercial Triticum aestivum wheat flour (locally named Setareh) was procured from the AceeArd Co., Khorasan, Iran. Propylene glycol (PG) was purchased from J.T. Baker Chemical Company (Phillipsburg, NJ). Sodium stearoyl-2-lactylate (SSL) and diacetyl tartaric acid esters of monoglycerides (DATEMs) were provided by Vista Tejarat Company (Tehran, Iran). Moisture, ash, fat, protein, wet gluten and falling number were determined according to standard AACC methods. Three replications were taken for each characteristic. Gel samples were prepared using sodium stearoyl-2-lactylate (SSL), diacetyl tartaric acid esters of monoglyceride (DATEM) and propylene glycol (PG) in the range of 0-0.5 g/100g. Bread making was carried out according to the method of Maleki et al. (1981). Quality analysis of fresh bread samples was carried out by measuring specific volume. Sensory attributes of bread were selected according to the Iranian flat bread evaluation method, including bread form and shape; upper surface property; bottom surface property; cavity and porosity; firmness and softness of texture; chewiness; odor, flavor and taste and overall quality score. Staling phenomenon and its changes were evaluated by penetration test after 1 hour, 3, 5 and 7 days. The average values of L*, a*and b* colors describing the outer crust regions were obtained. The crumb grain features were the mean cell area, porosity, and cell density. A central composite design was constructed using the software Design Expert Version and was used for sampling of different combination of gel constituents. In addition, Lack of fit, coefficients of determination (R2), adj-R2, coefficient of variation (CV) and significant probabilities were calculated to check the model adequacy. Multivariate correlation matrix, coefficients of determination and principal components analysis were performed by using Minitab 15 software.
The characteristics of the flour are in the range of typical values of medium strong flour, suitable for Iranian Barbari flat bread. The results showed dough adhesiveness was increased by SSL addition but it was decreased by quadratic effect of SSL like as resilience. All of three components to the gel formula caused decrement in the hardness, gumminess and chewiness. But the interaction of them influenced on them. On the other hand, although cohesiveness increased by addition of all components but influenced significantly by interaction of them. Dough mechanical properties were furthermore correlated with dough farinographic aspects, quality, sensory parameters, image processing and shelf life of bread. It was proved that principal components analysis (PCA) is able to extract relevant information and offer an easy and promising approach for the interpretation of dough mechanical properties and its correlation with other properties and dough and bread. Partial least squares regression (PLSR) models were applied to determine the relationships between dough mechanical properties and dough farinographic properties, bread quality, sensory, image processing and shelf life aspects. Results from statistical analysis suggest that the mechanical parameters of dough are capable in predicting more than 50% of dough and bread properties