INFLUENCE OF THE CHEESE ADDITION ON PHYSICOCHEMICAL AND TEXTURAL CHANGES IN WHEAT BREAD DURING FROZEN STORAGE

Grzegorz Szczepanik, Katarzyna Ptak, Robert Iwański
Department of Dairy Technology and Food Storage, West Pomeranian University of Technology, Szczecin, Poland

ABSTRACT

The aim of this study was to determine the effect of cheese addition on physicochemical and sensory changes in wheat bread, which were observed during 3 months of frozen storage. Cheese was added at 1, 5 and 10% levels to dough. The samples, after baking, cooling and freezing, were kept in the temperature of -25°C. The quailty of fresh bread and after 1, 2 and 3 months of frozen storage was estimated by determination of mass change, acidity, hardness, cohesiveness, springness, resilience, gumminess, chewiness and sensory evaluation.
Along with the increase of length of frozen storage period, weight losses of the examined samples, irrespective of the quantity of cheese addition, were increased. Whereas the presence of cheese in wheat bread caused a higher level of acidity. In the organoleptic assesment fresh bread and bread after 1 month of storage were obtained higher score, thus it can be classified among  the 1st class quality products. After 2 months of storage only the loaves with 5% cheese were assigned to the 1st class in sensory analysis.
On the basis of results obtained it was found that the addition of cheese resulted in the increase of hardness, cohesiveness, resilience, gumminess and chewiness and the decrease of springiness. Comparing the change of texture parameters of fresh and storing samples was affirmed the significant differences. Only the samples of bread with 1% and 5% addition of cheese did not show the essential change of hardness after whole their period the storage. The statistical analyses showed that acidity of bread correlated with texture parameters, including hardness and gumminess. It has been also found the high values of correlation coefficients between gumminess and chewiness, cohesiveness and resilience, hardness and gumminess/chewiness.

Key words: bread, frozen storage, chess, TPA.

INTRODUCTION

Cereals and cereal products such as bread contain many nutrients that are essential in the human diet. Bread is especially significant due to its popularity and scale of consumption. Undoubtedly, there exists a demand for obtaining and maintaining high quality in produced bread, including its sensory attributes, physiochemical characteristics and effect on human health [4]. Maintaining the freshness of the bread crumb is one of the most important quality parameters of bread which should correspond to the expectations and tastes of consumers. The loss of freshness may affect business due to an excess amount of unsold bread [34]. Hence the need for counteracting the process of bread ageing, including staling, moisture losses and redistribution, and enzymatic and microbiological transformations, exhibited by increased hardness and crumbliness, decreased crunchiness of the crust, loss of scent and other attributes of a fresh product [14].

The main goal of using low temperature bread storage should not be creating large reserves, rather achieving a balance between demand and supply that helps maintain a regular and reliable supply of a wide range of products [20]. The lifetime of frozen bread depends mainly on the type of bread and the applied additives, storage temperature, wrapping and defrosting conditions. The usefulness of frozen storage and storage stability should be determined individually for each type of bread [22].

The quality of bread is significantly affected by the elastoplastic transformations, which result in worse texture, increased hardness of crumb and the crust, and the increased crispiness of crumb. These changes are associated with structural alterations of starch and the loss of moisture during frozen storage [10].  The changes in moisture content of frozen bread depend on the storage temperature. Deep frozen storage at -25°C results in a lower loss of moisture than normal storage at -15°C [22].

Milk, dairy products and milk protein preparations used in bread production influence the rheological attributes of dough and increase its nutritious value [19,27].  For example, the addition of buttermilk or acid curd cheese may increase the biological value of protein and also increase the content of calcium, which neutralizes the acidogenic effect of cereal products [3].

In Great Britain, bread produced with the addition of milk and a milks product is called 'milk bread'. This term is used only for bread with a minimum of6 % dry milk mass (excluding fat) per dry bread mass. It includes two subgroups of milk bread: 'milk bread' (produced using full-fat milk, or powdered full-fat milk, or with the addition of skimmed milk and butter), and 'skimmed milk bread' (using skimmed milk). The production of milk bread is faster than other breads as the milk fat increases the penetration of heat inside a loaf [27].

Over recent years, the texture of food has become increasingly important for consumers and producers [25]. It is a sensory and psychological characteristic, dependent on the chemical composition, structural and rheological attributes of a given product. Exact determination of texture is especially crucial for research on the effects of technological processes on the quality of products, and for developing new technologies and new products. Very often the measure of the product quality, for producers, is texture [24].

Basic rheological tests can help determine the relationship between rheological parameters and dough composition and structure. Finding the balance between the elasticity and viscosity of wheat bread helps manipulate the attributes of bread in order to achieve the optimal effect [18]. A popular test of food texture is a compression test and its modifications; one important development of the test is a double compression test (TPA) [25].

The quality of bread may be improved by additives which enhance the production process, improve the content of nutrients and enrich the nutritious value of products. They may also help enlarge the range of bread types and improve their qualities. Especially notable are natural additives which are popular among health-conscious consumers for their effect on rheological, wholesome, nutritious and sensory qualities. Additionally, such additives do not have a harmful effect if overdosed in the production process [21].

Therefore in this paper we examine the effect of hard cheese on the physiochemical and sensory attributes of wheat bread over three months of frozen storage. All the analyses were performed on fresh product and after frozen storage.  We determined a difference in weight during frozen storage (sublimation) from 1 to 3 months of storage, titratable acidity, and changes in bread texture (hardness, cohesiveness, springiness, resilience, gumminess and chewiness). We also performed organoleptic assessment and statistical analysis to determine the significance of differences between the applied amounts of additive, and the significance of storage duration on changes in bread quality using a selected dose of hard cheese. Correlation coefficients were calculated to determine the relationships between the individual texture characteristics, and between these parameters and acidity.

MATERIALS AND METHODS

In this study, we examined bread produced at the Department of Refrigeration and Department of Food Science and Technology, West Pomeranian University of Technology in Szczecin using wheat flour (type 550), Dutch Gouda hard cheese, yeast, salt (NaCl), and water.

The ingredients were weighed electronically to an accuracy of 0.01 g. Bread was then produced with the addition of the hard Dutch cheese at 1%, 5% and 10% of dough mass ready for baking.  Bread without hard cheese served as a control sample.

Baking was carried out in compliance with ICC Standard No. 131 [16], using a direct method for both control bread and experimental breads. The dough was made in a CONTI mixer at 45 rpm. The ingredients were mixed in the following amounts: flour (413 g), water (268.5 g – 65% of flour weight), yeast (3% of flour) added as a water solution (using the already measured water), and salt (1.5% of flour weight) as a water suspension. The dough produced from the aforementioned ingredients was subjected to 2 h fermentation at room temperature and then mixed with hard cheese (already fragmented with a cheese grater with 1cm holes) using a Conti mixer at 45 rpm. Dough was formed into 700 g loaves and moved to aluminum moulds, then subjected to proofing at 30-40°C for about 40 min. After that time, the aluminum moulds were placed in an electric oven, Unox XF (Italy), at 220–240°C for about 40–45 min. Then the baked loaves were cooled in room temperature and cut into 10 mm slices using a Kalmejer slicer type KBR11. The sliced bread was packed into polythene (PE) bags , frozen and stored at -25°C for 1, 2 and 3 months.

Determination of sublimation loss
After 1, 2 and 3 months of frozen storage, the samples were taken out, unwrapped, and weighed electronically to an accuracy of 0.01 g to determine differences in weight resulting from storage (sublimation), then the samples were defrosted by air at 4°C until the product reached 4°C. Until the following texture test, the samples were stored in a freezer at 4°C.
Changes resulting from sublimation (B) were calculated according to the formula:

B  =  raw material weight – frozen material weight after frozen storage

Determination of acidity
25 g samples were weighed on a laboratory balance and then each moved to a 500 cm³ dry conical flask with a fitted rubber bottle stopper. Using a measuring flask, 250 cm³ of distilled water was taken and poured into the flask with the sample, which was then closed and intensely shaken for 2 min and put away. The action was repeated every 15 min for the next hour. Then the solution was sifted through a filter, and 50 cm³ of the resultant transparent liquid was taken with a pipette and put into two 100 cm³ conical flasks, with the addition of 3–4 drops of phenolphtalein. Titration was carried out using a 0.1 mol NaOH solution until achieving a pale pink colour that remained for 1 min. The titratable acidity is an arithmetical mean of the consumed NaOH (cm³) from the two titrations.

Tekstural analysis
Rheological tests were performed using a TA.XT texture analyzer (Stable Micro Systems Ltd., England) using a cylinder shaped Delrin tenon with a diameter of 0.5 inch (Part code P/0.5R). The test parameters were as follows: Pre-Test Speed –
1.0 mm·s^-1, Test Speed – 1.7 mm·s^-1, Post-Test Speed – 10.0 mm·s^-1, Distance – 5 mm, Time – 10 s, Trigger Force – 5 g.

The texture of bread was examined with regard to hardness, springiness, cohesiveness, gumminess, chewiness and resilience. Hardness was determined as the force required for expected deformation (on a curve, it is the point of maximal inclination during the first cycle of pressing). Cohesiveness was calculated as the product of surfaces determined by the curves of the first and second compression. Elasticity was the ratio of time measured from the second compression until reaching the maximal deformation during that cycle, and the time measured since the first cycle of compression until reaching the maximum deformation during that cycle. Cohesiveness was the quotient of the surface of the first compression cycle since the maximum and the surface area of this cycle until reaching the highest value. Gumminess was calculated as the product of hardness and cohesiveness, and chewiness as the product of hardness, cohesiveness and springiness.

Sample preparation for TPA measurement
10 mm bread slices were placed on the texturometer table. Nine pressings were carried out for each product maintaining distances between the consecutive measurements ≥ 12 mm and ≥ 10 mm from the edge of the material. The measurement data were processed with Exponent Stable Micro Systems version 2.0.7.0® and Microsoft Excel®.

Sensory assessment
Sensory tests were based on ICC Standard No. 131. Details of the process were in accordance with PN-96/A-74108 [29]. The tests were carried out by students and university employees. The assessment was carried out 24h after baking, and after 1, 2 and 3 months of frozen storage (after defrosting).

Based on the obtained quantity of points, bread class was determined. The total quantity was added 8 points, allowing for the fact that physiochemical attributes such as volume, moisture, acidity, concentrations of salt, fat and sugars, were in compliance with norm.

Statistical analysis
The purpose of statistical analysis was to validate the hypothesis that the type of packing method used resulted in differences in the sizes defined qualitative indicators tested samples.
The received results were worked out statistically with utilization of Excel and Statistica 8.0 programmes. The significant differences were marked with Tukey test with the level of significance p ≤ 0.05.

RESULTS AND DISCUSSION

The performed tests on wheat bread with and without the addition of hard cheese (Dutch Gouda) measured its quality, and thus showed the effect of the applied additive on the quality of wheat bread over three-months of frozen storage.

Acidity
The acidity of cereal products is one of the criteria used in the assessment of their expiry date. It allows the assessment of the product's freshness and indicates biochemical transformations occurring during storage [32]. Bread acidity characterized the quality of this product with regard to its taste and nutritional value. The human body does not tolerate bread with excess acidity well; consumption of such bread may result in stomach ailments [31]. In our study, the addition of hard cheese (1% and 5%) did not affect the acidity of fresh bread. A 10 % addition caused only a slight increase in acidity (Table 1).

Along with the time of frozen storage, the acidity tended to increase slightly, but its final value was within the norm. The greater the addition, the greater the acidity.  Filipcev et al. [11] also observed an increase in acidity, in their case induced by the addition of kefir grains.

According to Fik and Celej [10], the increase in bread acidity, as an indirect indicator of fermentation and biochemical transformations, showed a relatively small increase over the time of storage, but it did not have a significant influence on the taste and scent of the frozen products. The increase in acidity is proof of the process of starch hydrolysis in the site 1,4-α and 1,6-α-glycoside.

Taste and aroma
Other very significant organoleptic indicators of bread aging are changes in the olfactory and gustatory attributes [9]. Such transformations in frozen bread are usually greater than changes in physiochemical indicators [8]. The characteristic aroma and taste of fresh bread gradually disappears, and after some time of storage, it may become unpleasant and specific [10,20].

Directly after baking, olfactory substances are unevenly distributed. In the crust they originate mainly from complex reactions between sugars and nitric compounds, and also from the pyrolysis of flour components, and in the inside they are usually formed during dough fermentation. During cooling, volatile components condense and are adsorbed by starch or protein substances, while in the crust they are partially lost through evaporation. Some of them may be completely lost as a result of various chemical reactions and oxidation, and binding to starch which produces insoluble complexes with no olfactory significance. The aroma and taste of baking products are therefore more complex at the beginning of the aging process than later [9]. It explains why in our experiment the taste and aroma of fresh bread with a 5% and 10% addition of hard cheese did not receive full approval ratings in organoleptic assessment. It might have resulted from the sensed specific taste and aroma of cheese. After a month of frozen storage, after the intensity of this taste and aroma had decreased, the rates were higher. After three months of frozen storage, the taste and aroma of bread with hard cheese added were assessed higher than the control bread (the highest for bread with 1 % additional hard cheese) (Table 2). The increasing amount of various additives used in bread baking may be sensed by customers and not necessarily well received. For example higher doses of lupin flour result in a slight bean-like aftertaste and aroma [5].

Dairy products (whey, buttermilk, sour milk, protein preparations) improve the taste and aroma of bread [21]. Milk bread has a characteristic aroma appreciated by most consumers, and a refined taste [11,27,28].

Appearance
When buying bread, consumers pay attention to other attributes, such as appearance, freshness, and general appeal, which shows in various shapes, wrappers, etc. The appearance of the examined samples slightly decreased with the increasing addition of cheese, but the 10% addition preserved the appearance best over the time of frozen storage. At the end of storage, bread showed only minimum deformation.

An important part in the formation of bread structure, and especially its colour, is played by lactose, an ingredient of milk and dairy products. This sugar participates in the reactions with proteins, thus influencing bread colour and taste, especially white bread [17]. The brown colour of the crust is brighter and more homogenous, as the production of Maillard's compounds (that are responsible for the brown colour) is more regular and less intense in the presence of lactose than in the presence of sacharose and glucose [27]. After the period of storage, the crust received worse ratings in organoleptic assessment, but the addition of cheese (and thus lactose) helped maintain its colour and thickness better.

Inside's texture
As indicated by Kawka and Flaczyk [19], the addition of dairy products affects the attributes of dough and bread's sensory characteristics. Their addition improves the structure of the inside (increased springiness and porosity), its hydrophilicity and viscosity [19,21]. Accordingly, the addition of cheese helped maintain the springiness of the inside after frozen storage, and the best springiness and porosity was the bread with 5% addition of hard cheese.

The main reasons of staling are transformations that occur in starch. During cooling and storage, the amorphous structure of starch in fresh bread, formed by gelatnization, creates a systematic crystalline net, which is accompanied by the release of water. These changes, called the retrogradation of starch, induce the hardening and crumbling of bread. The less water that has been absorbed by the dough, the faster the retrogradation [30].

In order to track the process of aging in the examined breads, we stored them in stable conditions for three consecutive months. The analysis of changes in mass showed that the loss of water over the whole storage was small (by 0.12-0.94%) both in standard bread and in breads with the addition of hard cheese.

Hard Gouda Cheese, used as an additive to wheat bread contains 45% fat in dry mass. Milk fat, most present in cheeses (20-30%) is characterized by a domination of short-chain saturated fatty acids and oleic acid and the presence of cholesterol and natural trans isomers. Milk fat is also the carrier of vitamins A and D [13].

Fats, 1-5% in relation to flour weight, are a commonly used additive in baking. Appropriately applied, they help model the physical characteristics of dough, the structure of the bread inside and its sensory characteristics. The induced changes result from the interactions between the proteins and fats. The change in spatial organization of the protein-fat complex increases the rheological attributes of bread. They are a consequence of the increased number of hydrophobic bonds that replace part of the hydrogen bonds responsible for the stability of the gluten structure in bread [26].

Monoglycerides of fatty acids protect starch against retrogradation (recrystallization) in a ready product being the main reason for bread staling [35].

The hardness of bread, the measure of its freshness, increased in frozen storage, and along with the increase of hard cheese. However, after the third month it decreased, and was even lower than initial hardness, except the control sample whose hardness was higher than initially. It may have resulted from physiochemical changes that occurred during the entire duration of storage. However, both in fresh samples and after 3 months of storage, the increase in additive induced an increase in hardness (Fig. 1).

An increase in hardness over storage was also observed in the application of additives such as kefir [7], buckwheat flour [6], green tea extract (GTE) [33].

A advantageous effect on the inhibition of the crumb staling was also observed after the addition of amaranthus flour [31] and the addition of sodium alginate [15] and hydroxypropylmethylcellulose (HPMC) [2,15].

Over the period of frozen storage of wheat bread with the addition of hard cheese, the cohesiveness of bread decreased (Fig. 2).  In fresh samples the addition of cheese decreased the cohesiveness, except the 1% addition samples which had cohesiveness higher than control. However, at the end of frozen storage, all the samples with addition had higher cohesiveness than control. It was confirmed by Korzeniowska-Ginter [21] which reports that fats and their derivatives improve the cohesiveness of dough. Dziki and Laskowski [6] showed that the addition of buckwheat flour to wheat flour decreased the cohesiveness of dough.

The springiness of bread with and without the addition of hard cheese slightly decreased along the time of frozen storage. At the end of storage, control samples showed higher springiness in comparison with samples with the addition of hard cheese, the springiness of which decreased with the increase in the addition of hard cheese. We did not achieve the increase in springiness that was achieved by Lewicka and Abramczyk [23] who used ascorbinate acid.

The results of wheat bread resilience with and without the addition of hard cheese showed its significant decrease over the period of frozen storage (Fig. 3). At the end of storage all the samples with hard cheese showed a higher resilience than samples without the addition. The increase in resilience was also observed after the addition of buckwheat flour [6] and amaranth flour in addition to wheat flour [31], and also ascorbinate acid [23]. However, the addition of flour made from Lathyrus sativus seeds lead to a decrease in resilience of the bread inside [1].

The gumminess of wheat bread with and without the addition of hard Gouda cheese decreased over the period of frozen storage. Generally, the gumminess of bread increased with the increase in the amount of the added cheese. A similar increase in the inside gumminess could be induced by an increase in the addition of buckwheat flour to wheat flour [6] and with the participation of ground and scaleded flax seeds [12]. Such an increase was also observed by Diowksz et al. [5] using lupin flour in the recipe of gluten-free bread, which is a common drawback of this kind of bread. However, in breads with the addition of dry ground flaxseed a progressing decrease in gumminess was observed [12].

The results of wheat bread chewiness with and without the addition of hard cheese during frozen storage show its decrease with time. The chewiness of bread, similar to the hardness and gumminess, increased with the amount of the applied additive. An increase in chewiness was also observed by Esteller et al. [7] using the addition of kefir, Gambuś et al. [12]  in breads with ground and scalded flax seeds, and Dziki and Laskowski [6] where the increase in chewiness was observed along with the increase in the addition of buckwheat flour to wheat flour.

Statistical analysis
The hardness of probes increased with storage time and percentage adding of cheese. In the control probe average hardness were 2.3 [G] for 1% of cheese additive, 3.8 [G] for 5% of cheese and 4.4 [G] for 10% of cheese additive. The results were statistically significant (Α ≤ 0.05) in Tukey test. The two months storage process caused increasing of hardness to control about 1÷1.5 [G] however not affirmed statistically different between results. After three months storage processing the higher hardness compare to control average about 0.3 [G] were observed. Influence of percentage concentration of cheese additive was not statistically significant but increased (average 0.2 [G]). The correlation analyses proved that progress of hardness changes were correlated with two months storage, but hardness were lover in three months storage time (Fig. 4). 

The significant, compare to control decrease of chewiness was reported in bread after three months storage time and all percentage concentrations of cheese in dough, although the chewiness of 10% additive of cheese was higher to control (0.05 [G]), but not significant statistically. In other cases chewiness increased. A similar situation was observed in gumminess case (Fig. 5).

The other reological tests: resilience (Fig. 6), cohesiveness and springiness demonstrate decreasing and statistically significant trend of results compare to control.

CONCLUSIONS

During a three month long frozen storage of wheat bread with and without the addition of hard Gouda cheese, we observed only a slight increase in acidity. However, its final value was within norm. The addition of hard cheese did influence the organoleptic assessment of bread. After a three month long frozen storage, the 10% addition of cheese helped maintain the best appearance of bread and crust thickness. Bread with 5% addition had the best colour of crust, and the best resilience and porosity of the inside. However, the bread with 1% addition had the most desired taste and scent.

Ultimately applied add cheese (as compared to samples without added) helped to improve the rheological parameters such as cohesiveness and resilience. Has slightly worsened while springiness, hardness and gumminess and chewiness.

REFERENCES

1. Achremowicz B., Korus J., Curylo K., 2000. The effect of different pulse additives to bread products. EJPAU, Food Sci. Technol. 3(2), www.ejpau.media.pl.

2. Barcenas M.E., Rosell C.M., 2005. Effect of HPMC addition on the microstructure, quality and aging of wheat bread. Food Hydrocoll. 19(6), 1037-1043.

3. Bartnikowska E., 2007. Dodatki do pieczywa o działaniu prozdrowotnym [Beneficial additives in bread production]. Przegl. Piek. Cukier. 55(8), 4-9 [in Polish].

4. Ceglinska A., Haber T., 2006. Niektóre problemy piekarstwa oraz możliwości wykorzystania nowych surowców [Selected problems of the baking industry and the potential use of new ingredients]. Skrót wystąpienia na Seminarium zorganizowanym w Mszczonowie, Poland, 17.05.2006. [in Polish].

5. Diowksz A., Kajzer M., Zajac T., 2007. Mąka łubinowa w recepturze chleba bezglutenowego [Lupin flour the recipe of non-gluten bread]. Przegl. Piek. Cukier. 55(10), 8-12 [in Polish].

6. Dziki D., Laskowski J., 2005. Wpływ dodatku mąki gryczanej do mąki pszennej na wybrane cechy ciasta i miękiszu pieczywa [The effect of buckwheat flour addition to wheat flour on the selected attributes of dough and bread inside]. Acta Agrophys. 6(3), 617-624 [in Polish].

7. Esteller M.S., Zancanaro O., Palmeira C.N.S., Lannes S.C.S., 2005. The effect of kefir addition on microstructure parameters and physical properties of porous white bread. Eur. Food Res. Technol. 222, 26-31.

8. Fik M., Celej A., 1992. Zmiany jakości bułek podczas zamrażalniczego przechowywania [Changes in the quality of bread rolls during frozen storage]. Chłodnictwo 27(1), 26-28 [in Polish].

9. Fik M., Celej A., 1993. Niektóre aspekty czerstwienia pieczywa i sposoby jego powstrzymywania [Selected aspects of bread staling and methods of bread staling prevention]. Chłodnictwo 28(1), 29-31 [in Polish].

10. Fik M and Celej A, 1993. Zmiany jakości pieczywa podczas zamrażalniczego przechowywania [Changes in the quality of bread during frozen storage]. Chłodnictwo 28(3), 32-34 [in Polish].

11. Filipcev B., Simurina O., Bodroza-Solarov M., 2007. Effect of native and lyophilized kefir grains on sensory and physical attributes of wheat bread. J. Food Process. Preserv. 31(3), 367-377.

12. Gambuś H., Gambuś F., Borowiec F., Zając T., 1999. Możliwość zastosowania nasion lnu oleistego w piekarstwie [The application of flaxseed in baking]. ZNAR Krak. Technol. Żywn. 11(360),  83-94 [in Polish].

13. Gawęcki J., Hryniewiecki L., 1998. Żywienie człowieka. Podstawy nauki o żywieniu (I) [Human nutrition. Basics of nutrition]. PWN, Warsaw, Poland 310-313 [in Polish].

14. Gruda Z., Postolski J., 1999. Zamrażanie żywności [Food freezing]. WNT, Warsaw, Poland, 339-345 [in Polish].

15. Guarda A., Rosell C.M., Benedito C., Galatto M.J., 2004. Different hydrocolloids as bread improvers and antistaling agents. Food Hydrocoll. 18(2), 241-247.

16. ICC Standard No. 131. Metod for Test Baking of Wheat Flours.

17. Janitz W., Gorecka D., 1999. Wykorzystanie koncentratów i izolatów białek mleka w produkcji pieczywa i wyrobów cukierniczych [The application of milk protein isolates and concentrates in the production of bread and confectionery]. Przegl. Piek. Cukier. 47(4), 12-13 [in Polish].

18. Jarosz K., Paschke H., 2003. Wpływ tłuszczów i hydrokoloidu oraz sposobu ich wprowadzania do ciasta na uzyskany efekt technologiczny w piekarstwie [Effects of fats and hydrocolloid and how they are placing on the dough, the resulting effect of technological advances in baking]. Przegl. Piek. Cukier. 51(8), 2-6 [in Polish].

19. Kawka A., Flaczyk E., 2000. Dodatki technologiczne wzbogacające pieczywo [Technological additives in bread production]. Przegl. Piek. Cukier. 48(5), 8-10 [in Polish].

20. Kondratowicz J., Chwastowska I., 2006. Wpływ różnych technologii chłodniczych na jakość wyrobów piekarniczych [The effect of various frozen storage technologies on the quality of bakery products]. Chłodnictwo 41(8), 36-41 [in Polish].

21. Korzeniowska-Ginter R., 2006. Naturalne dodatki i uszlachetnianie pieczywa [Natural additives and bread enhancement]. Inz. Aparat. Chem. 37, 1-2, 50-52 [in Polish].

22. Krala L., Kulagowska A., 2002. Wpływ temperatury zamrażalniczego przechowywania na jakość pieczywa uszlachetnionego ziarnami zbóż [The effect of the temperature of frozen storage on the quality of bread with cereal sedes]. Chłodnictwo 37(9), 36-39 [in Polish].

23. Lewicka B., Abramczyk D., 2007 Wpływ dodatku kwasu askorbinowego na cechy ciasta i jakość pieczywa pszennego [The influence of ascorbinate acid on the attributes of dough and the quality of wheat bread]. Przegl. Piek. Cukier., 55(11), 20-24 [in Polish].

24. Marzec A., 2007. Tekstura żywności [Food Texture]. Prz. Spoż. 61(5), 6-10 [in Polish].

25. Neryng A., Grzesinska W., Rutkowska J., Pacholczyk E., 1996. Pomiar wybranych właściwości fizycznych (tekstury) gotowanych warzyw [Measurement of selected physical attributes (texture) of boiled vegetables]. Z. Pr. Post. N. Roln. 430, 31-35 [in Polish].

26. Paschke H., Jankiewicz M., 2002. Wpływ dodatku tłuszczu na właściwości lepkosprężyste ciasta pszennego [The effect of fat on the viscosity and springiness of wheat bread]. Żywn. N. Technol. Jak. 3(32), 127-135 [in Polish].

27. Piesiewicz H., 2006. Chleby mleczne [Milk breads].  Przegl. Piek. Cukier. 54(9), 50-52 [in Polish].

28. Plessas S., Pherson L., Bekatorou A., Nigam P., Koutinas A.A., 2005. Bread making using kefir grains as baker's yeast. Food Chem. 93(4), 585-589.

29. Polish Norm PN-96/A-74108: Pieczywo. Metody badań [Bread. Research Methods]. [in Polish].

30. Słowik E., 2002. Przedłużanie świeżości i trwałości pieczywa – dodatki i sposoby [The extension of bread freshness and life – additives and techniques]. Przegl. Piek. Cukier. 50(6), 14-17 [in Polish].

31. Sobieraj I., Rawski J., 2002. Badanie wpływu mąki z amarantusa na jakość pieczywa pszennego [The effect of amaranthus flour on the quality of wheat bread]. Przegl. Piek. Cukier., 50(8), 10-12 [in Polish].

32. Szafranska A., 2007. Metody oznaczania kwasowości przetworów zbożowych [Methods of acidity determination for cereal products]. Prz. Zboż. Młyn. 51(10), 15-16 [in Polish].

33. Wang R., Zhou W., Isabelle M., 2007. Comparison study of the effect of green tea extract (GTE) on the quality of bread by instrumental analysis and sensory evaluation. Food Res. Int. 40(4), 470-479.

34. Wybierala A.R., 2006. Od ziarna do dobrego chleba – cz. XV: Jakość surowca a świeżość [From seed to good bread – part 15: Material quality vs. Freshness]. Cukier Piek, 10(9), 72-74 [in Polish].

35. Zawadzki K., 2005. Polepszacze jakości pieczywa – działanie i zakres stosowania [Bread improvers – effect and range of application]. Prz. Zboż. Młyn. 49(7) 16-17 [in Polish].

Accepted for print: 16.02.2010

Responses to this article, comments are invited and should be submitted within three months of the publication of the article. If accepted for publication, they will be published in the chapter headed 'Discussions' and hyperlinked to the article.