SELECTED PROPERTIES OF FROZEN BAKERY PRODUCTS WITH AN ADDITION OF SPELT WHEAT AND SORBITOL

Katarzyna Kozłowicz¹, Franciszek Kluza^2
1 Department of Refrigeration and Energetics of Food Industry, Agricultural University in Lublin, Poland
² Department of Refrigeration and Food Industry Energetics, University of Life Sciences in Lublin, Poland

ABSTRACT

The studies concerned enriching bakery products with selected ingredients with pro-health properties and a simultaneous estimation of their effect on the physical (weight loss, the proper weight of the crumb, the proportion of crust to crumb) and sensory properties of bakery. The analyses showed the effect of the kind of ingredient and its weight share on the characteristics of the test baking. Independently of the kind of bakery product, its freezing did not influence the studied physical properties. The identified weight losses depend on and are an effect of the manner of thawing. Thawing in a microwave oven caused much greater weight losses than in the case of thawing in the air, and it did not cause any significant change in the examined properties. However, changes were found in the proper weight of the crumb, the proportion of crust to crumb; besides, the elasticity of the crumb and the hardness of the crust were decreased, which had an effect on the value of organoleptic evaluation.

Key words: refrigerating and defrosting of bakery products, pro-health additives.

INTRODUCTION

The problem of fresh bakery products is at present dominating on the food market and it should be expected that in the future its importance will grow together with the consumers’ increasing demands. Changes in their interests enforce the application of treatments that increase the durability of final products. One of such treatments is processing the products including freezing and freezing storage of both baked products and semi-products in the form of frozen dough or partly baked dough [1,4,7]. Besides, bakery products are more and more frequently modified, in the direction of lowering the caloric content in return for increased nutritious value. Food with prophylactic and dietetic effects has a greater and greater share on the market. The basic criterion of choosing the substances added to bakery products is their safety for man’s health and the proved technological reasons for their application. To this aim, natural products are used which lengthen the durability of a product and increase its taste. Properly applied, they have a positive effect on the properties of dough, they reduce the changes that take place during storage and make it possible to widen the assortment of bakery products and make the latter more attractive [2,5,8,9].

The purpose of the investigation was to characterize some selected pro-health ingredients on the quality properties of frozen bakery products, evaluated considering their thawing in differentiated conditions.

MATERIAL AND METHODS

The studies examined bakery products prepared according to the following technological recipe: what flour type 550 100%, fat powdered milk 3.8%, saccharose 5.8%, salt 1.7%, dry yeast 0.9%, cinnamon 0.3%, ascorbic acid 0.04%, water 68.2%, plant oil 5.5%. The basic recipe was modified by replacing wheat flour with spelt wheat flour and a combination of spelt wheat flour and sorbitol (Table 1).

The studies were based on processing dough with the direct method, which consists in simultaneous addition of all elements from the recipe to flour, and mixing them carefully. The dough was divided into mouthfuls of 250 g, and subjected to fermentation. A test baking was performed in an electrical oven at the temperature of 220°C for 20 minutes.

The products freezing time was determined from the obtained data, on the basis of which an exemplary freezing curve was prepared using a Microsoft Excel program. The obtained freezing curves of the control sample were used to establish its cryoscopic temperature T_cr. The frozen products were packed in PE foil and stored for 2 weeks in the air of the temperature of -30°C. The thawing process was conducted in two ways: by blowing the air at room temperature and in a microwave oven. The analysis of physical changes was performed both for the products that were not frozen and for thawed ones.

Determination of the crumb acidity of the bakery products was conducted using a pHmeter ELMETRON, CP-401 with a combined electrode pH type OSH 12-00 with accuracy ±0.05. The arithmetic means from three measurements was taken as an result.

At the same time, organoleptic evaluation was made of the colour, taste, porosity and general appearance in a 40-degree scale according to the norm PN-79/A-74108. The results present average values obtained for at least three samples taken for studies [3,6].

RESULTS AND DISCUSSION

From the analysis of the obtained data follows that the cryoscopic temperature of the control samples of the examined bakery products was T_cr = -5.5°C, and its freezing time 1.5 hours until the temperature of -18.0°C was obtained.
A test baking characterized a set of features that determine the quality of bakery products (Table 2).

It showed that the proportion of spelt wheat flour (as a substitute for wheat flour) and a modification with spelt wheat flour and sorbitol (as a substitute for saccharose) affected increased productivity as compared to the control group. Together with an increasing share of the applied additives, the values of the examined features grew. Bakery products with 100% sorbitol and 60% of spelt wheat flour were characterized by the greatest productivity of dough (209.5%) and that of the products (190.98%). It follows from the obtained data that the products with 80% of sorbitol and 60% of spelt wheat flour (4.8%) were characterized by the least baking efficiency, while the products with 40% of spelt wheat flour (9.8%) was characterized by the highest efficiency. Besides, the volume of the obtained products decreased together with an increasing proportion of both spelt wheat flour and sorbitol.

The final result of the estimation of the quality of bakery products obtained from test baking is the number of the value of bakery products (LWP), which also constitutes an estimation of the quality of the used flour. The highest LWP was obtained for control bakery products (113) and for the sample modified with 20% of spelt wheat flour (100). This indicator makes it possible to classify these samples to the group of bakery products of very good quality features. An increased share of spelt wheat flour and its combination with sorbitol decreased the number of the value of the products. Those with sorbitol were characterized by the lowest LWP value. The LWP value at he level of 59 (20% of sorbitol and 60% of spelt wheat flour) means that a modification with good baking characteristics was used.

Acidity of bakery products characterize the quality of these products from the point of view of their taste. Acidity of the control sample and a sample modified with a 20% share of spelt wheat flour was 2.9°. Together with an increased share of both spelt wheat flour and sorbitol the acidity of bakery products increased. The highest acidity of bakery products at the level of 5.8° was observed for the sample modified with spelt wheat flour in the quantity of 60% and sorbitol 80%. Despite considerable differentiation of the acidity level between the control sample and the other samples, an increase of this index had no effect on the taste and flavour of the bakery products judged by means of sensory evaluated.

It follows from the studies that the very process of freezing and a short-time storage (2 weeks) did not significantly affect changes of the weight of the studied products. After thawing, the studies observed slight differences in the weight of the bakery products in relation to the control sample that was not frozen.

Weight losses, which means the differences between the weight of unfrozen products and the weight of frozen ones which appeared as a result of microwave heating, were much bigger than in the case of traditional thawing of bakery products in the air at room temperature (Fig. 1). For the products baked with a 60% share of spelt wheat flour they were on the level of 1.2%, while after traditional thawing the weight loss of these products was only 0.13%.

The weight of the proper crumb, like the volume, depends first of all on the course of the technological process. This feature is of special importance while comparing the quality of bakery products of the same kind. It was found out that the thawing process had only a slight effect on the change of the proper weight of the crumb of the obtained product. This feature underwent small changes as compared to the control: with the increasing weight of the chosen ingredient, the value of the examined feature had an increasing tendency (Fig. 2). After air thawing, the greatest proper weight (0.38 g·cm^-3) was observed for the products with a 20% share of spelt wheat flour, and the smallest (0.27 g·cm^-3) for those with a 40% share of spelt wheat flour.

A negative phenomenon in frozen bakery products is frequent coming off of the crust from the crumb. This is affected, for example, by the kind of product, its freezing rate, the storage conditions and migration of moisture in the sub-crust layer, which leads to its reduction in the crumb and growth in the crust. It is assumed that depending on the kind of products the crumb constitutes from 60% to 90% of the total weight. This points to the temperature and time of baking. After air thawing, a change was observed in the proportion between the crust and the crumb, independently of its kind and the proportion of the applied thawing (Fig. 3). Microwave processing affected the proportion between the crust and the crumb in the way comparable to the values obtained as a result of traditional defrosting. An exception are the samples with a 20% and a 40% share of spelt wheat flour, where the studies observed a considerable drop of the proportion between the crust and the crumb as regards the bakery products thawed in a microwave. An increase of this value was found out in the products baked with a modification of 100% sorbitol addition and spelt wheat flour.

The sensory analysis (Fig. 4 and Photo 1) found out that bakery products with a 20% addition of spelt wheat flour had the highest quality and received the highest score (40). Those products were well risen and had the proper shape slightly resembling the shape of the mould. The crumb was characterized by even light-cream or dark-cream colour, depending on the additive. It also had even porosity, proper moisture and very good elasticity. The crust had the proper thickness, colour and appearance. The products also had the proper taste and a characteristic aroma. On the other hand, the products modified with a 100% share of sorbitol and with a 60% addition of spelt wheat flour were characterized by fairly even crumb and only sufficient elasticity, which caused that they received the smallest score (34) and were classified in class II of quality.

Freezing bakery products and thawing them in the air mainly decreased their elasticity in the case of products with 50%, 80% and 100% sorbitol. Besides, they were characterized by hardly felt smell and sweetness, which caused that in the sensory evaluation they received the scores of 35 and 34 and were placed in class II of quality.

Freezing and thawed bakery products using a microwave oven first of all affected worse elasticity of the products with a modification of sorbitol and spelt wheat flour. Those products were placed in class II of quality as in the sensory evaluation they got the scores ranging from 32 to 35.

CONCLUSIONS

1. The cryoscopic temperature of frozen bakery products was T_cr = -5.5°C and their freezing time till the temperature of -18°C reached by the thermal center of product was 1.5 hours.

2. The products obtained with a 60% share of spelt wheat flour were characterized by the highest productivity of 162.02% and the smallest oven loss of 7.12%. The higher the weight share of spelt wheat flour in the products, the smaller their volume, the greater the proper weight of the crumb and the smaller the relation between the crust and the crumb.

3. Air thawing of bakery products did not cause any significant changes of the selected physical and organoleptic properties. Microwave thawing affected worse elasticity of the crumb and smaller proper weight.

4. The obtained bakery products were characterized by the proper shape, even, porous crumb, very good elasticity, taste and a very nice aroma. In the organoleptic evaluation the highest score (40) was received by the products with a 20% share of spelt wheat, whereas the lowest (32) by the products thawed in a microwave with a 100% share of sorbitol and a 60% share of spelt wheat.

5. Considering the quality properties of bakery products, such as productivity and volume of the products as well as some chosen physical properties of thawed products, the best influence was exerted by spelt wheat flour in the proportions of 20% and 40%.

REFERENCES

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Accepted for print: 10.03.2008

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