THE EFFECT OF STARTER INOCULATION TYPE ON SELECTED QUALITATIVE ATTRIBUTES OF ACID CURD CHEESES [TVAROGS] STORED UNDER COOLING CONDITIONS

Izabela Dmytrów¹, Krzysztof Kryża¹, Krzysztof Dmytrów^2
1 Department of Dairy Technology and Food Storage, West Pomeranian University of Technology, Szczecin, Poland
² Department of Econometrics and Statistics, Faculty of Economics and Management, University of Szczecin, Poland

ABSTRACT

The effect of two lyophilised starter inoculations FLDAN and CHN-11 of Danisco Biolacta manufacture on organoleptic attributes and selected physical and chemical indices of curd cheeses [tvarogs] was analysed. The cheeses produced under laboratory conditions were vacuum-packed in polyethylene foil and stored for 5 weeks at 5°C [± 1°C]. The examined cheeses were assessed organoleptically as well as water, fat and protein contents, titratable acidity and pH, and fat oxidation changes were determined in them. Moreover, cheese hardness was determined by means of double compression test [TPA]. It was found that during the storage the curd cheese produced using FLDAN starter inoculation was characterised by better organoleptic attributes and lower whey leakage. The type pf starter inoculation did not differentiate significantly the produced cheeses in respect of fat and water contents nor affected titratable and active [pH] acidity of the analysed samples either. The used starter cultures affected however the hardness of examined curd cheeses. Higher hardness in the whole study period was a characteristic of the curd cheese manufactured with FLDAN starter culture. Also slower fat oxidation to primary and secondary products occurred in this cheese in the whole storage period. Moreover, the type of curd cheese inoculation used did not produce differences in the course of changes in the content of conjugated fatty acids [dienes and trienes].

Key words: curd cheese [tvarog], inoculations, acidity, fat oxidation.

INTRODUCTION

The most important stage in production of curd cheeses [tvarogs] is to obtain a clot of appropriate consistency. The proper course of technological process is affected by factors that are connected with raw material quality and production conditions as well as with application of cheese starters of good quality. Cheese starter added to the milk for cheese-making allows for proper orientation of fermentation processes and ensures characteristic organoleptic attributes given to cheeses. The selection of most suitable starter culture for manufacture of a specific product depends on many parameters connected with the production itself as well as with properties of the applied starter culture. These parameters interact together [2, 6, 7, 14]. Chemical transformations of respective components that take place during the storage are also of importance. Despite the fact that milk fat is poor in polyenic acids (to about 3.0%) [1, 36, 32], diary products are exposed however to oxidation changes that occur both during production and storage. It can not be excluded that oxidation processes may depend on the type of applied starter cultures and the method of curd cheese production.

The aim of carried out research work was to determine the effect of the type of applied starter culture on organoleptic attributes and physical and chemical changes in acid curd cheeses during storage.

MATERIAL AND METHODS

Research material consisted of acid curd cheeses produced under laboratory conditions using two different starter cultures [FLDAN and CHN-11] according to production technology instruction “Non-maturating curd cheeses ” No. 342/88 vacuum-packed in 40 µm PA/PE foil. The raw material for production of curd cheeses was high temperature pasteurised homogenised consumption milk with 3.2% butter fat, 3% protein and 4.3% lactose, manufactured by the Regional Dairy Cooperative in Krosno Odrzańskie.

In order to obtain curd cheese clot, two types of lyophilised mesophilic aromatic dairy starter cultures LD were used in the form of DVS, i.e. FLDAN [Flora Danica Normal] and CHN-11, of Danisco Biolacta Sp. z o.o. manufacture. Both cheese variants were produced with identical production technology parameters maintained.

The dairy starter cultures used contained the following set of bacterial strains: Lactococcus lactis subsp. lactis, Lactococcus lactis subsp. cremoris, Leuconostoc mesenteroides subsp. cremoris and Lactococcus lactis subsp. lactis var diacetylactis, with total cell concentration of minimum 5 x 10¹⁰ cfu/g and high production of aroma and CO₂ and medium proteolysis. The applied diary starter cultures differed between each other in the amount of used Lactococcus lactis subsp. diacetylactis. The FLDAN starter inoculation contains 5-30% Lactococcus lactis subsp. diacetylactis, whereas CHN-11 inoculation has 5-40% of that strain. The FLDAN starter culture is a high-aromatising inoculation, particularly useful for production of traditional curd cheeses, butter and sour cream, whereas CHN-11 inoculation is recommended for production of fermented dairy products and butter. The analysis of curd cheeses was made directly after their production and after 3, 7, 14, 21, 28 and 35 days of storage at 5°C±1°C. In total, 24 wedge-shaped portion of curd cheese were stored. The produced cheese was vacuum-packed. In vaucum-packing system, negative pressure of 15 mbar was used for 2.5 s and “soft-air” option at 400 mbar. The curd cheeses sampled for the analysis underwent each time organoleptic evaluation with the use of five-point scoring scale [24, 25]. The cheese consistency, colour and taste and aroma were determined according to criteria presented in Table 1. The evaluation was made by a 5-person panel trained in carrying curd cheese sensory analysis. Samples for the analysis were collected randomly. Examination was carried out in a room free from foreign odours, where each taste panel member had a separate test stand and enough distilled water for mouth rinsing.

In the analysed curd cheese variants were determined according to the Polish Standard [23]: water content by the drying method, fat content by the Gerber method, titratable acidity in °SH and pH. Additionally, protein content in experimental samples on production day and after 21 and 35 days of storage wad determined with Kjeldahl method.

The oxidation changes in curd cheeses were determined in the fat extracted with a mixture of chloroform and methanol [2:1] according to the Bligh and Dyer method with modification of Linko [18]. In the chloroform horizon of extracts were determined: content of hydroperoxides with indirect method after their oxidation to malonic aldehyde [MA] using FeCl₃ and TBA reaction [28], content of conjugated diene and triene structures of fatty acids diluted to 1:10 to 1:20 by absorbance measurement, content of chloroform extracts at a wave-length of 240 nm and 278 nm, respectively, and then calculating the coefficient of absorption [21]. The methanol-aqueous horizon of extracts was used for determination of secondary oxidation products [malonic aldehyde] with TBA by the method described by Schmedes and Hølmer [28].

The experimental acid curd cheeses underwent also a rheological analysis, which was based on the evaluation of their hardness [26]. This analysis was made by means of double compression test TPA using a texture analyser TA.XT Plus of Stable Micro System manufacture. The obtained results were analysed statistically with the use the t-Students test, Cochran-Cox test and Shapiro-Wilk’s test using Microsoft Excel 2000 software package. All test were made at significance level α = 0.05.

RESULTS AND DISCUSSION

The carried out score organoleptic assessment showed the influence of used starter culture on organoleptic attributes of the experimental curd cheeses. The examined curd cheeses were characterised by appropriate organoleptic attributes with the largest differences being found in the taste and aroma and the consistency of analysed samples [Fig. 1].

The evaluating test panel selected the curd cheese produced using FLDAN starter culture as the most desired one. As the storage time passed, a gradual deterioration occurred of organoleptic attributes in the samples analysed. On the last storage time, the taste and aroma of cheese A [with FLDAN starter culture] was scored at 2.8 points only, whereas its consistency to 3 points. Cheese B [with CHN-11 starter culture] received only 2.5 points for both features in similar time. No changes were observed in the colour of curd cheeses analysed. It continued to be uniform chalk-white, in the whole study period. Żuraw et al. [37] also found that curd cheeses obtained using DVS FLDAN concentrate were characterised by considerably better organoleptic attributes when compared with those received using DVS CHN-11 concentrate. Bonczar et al. [2] showed, when carrying out examination on sheep cheeses, a significant effect of the type of applied starter inoculation on the shaping of cheese sensory attributes. They found that result of sheep cheese organoleptic evaluation worsened together with the lapse of time. According to them, thermophilic and mesophilic bacilli differ in fermentative, proteolytic and lypolytic activity, which changes during the storage of milk and its products. The changes observed in the consistency of experimental curd cheeses are confirmed by the research work of Smietana et al. [31]. The sensory analysis of curd cheese performed by the test panel mentioned above showed that the product was highly stabile in respect to organoleptic attributes during 15 cool storage days. The outward appearance of tvarog did not change, whereas its consistency became firmer. The differences observed in the shaping of consistency of experimental curd cheeses may be explained by different quantitative participation of flavouring additives in the cheese leavens applied. According to Roczniakowa [27] and Birkkjear et al. and Stadhouders [after [35]], it is recommended to control in cheese-making inoculations the content of flavouring strains L. lactis subsp. lactis var. diacetylactis and Leuconostoc [not more than 15-20% in relation to other strains], as these strains, producing CO₂, in extreme cases may result in a swollen, porous clot and inferior consistency. Therefore, it may be supposed that the curd cheese produced with participation of CHN-11 starter culture [cheese B] could contain more bacteria responsible for aroma production when compared with cheese A. The use of strains of genus Leuconostoc contributes also to softening the product taste and aroma through transformation of acetic aldehyde [ethanal] produced by L. lactis subsp. lactis var. diacetylactis into ethanol [ethyl alcohol].

In the examined acid curd cheeses, mean protein content amounted to 15.56% for cheese A [FLDAN starter culture], whereas to 16.05% for cheese B [with CHN-11 starter culture]. Kolanowski [15] reports that mean protein content in half-fat acid curd cheeses should amount to 16.7%. Smietana et al. [30], testing production technology of acid curd cheeses, reported protein content from 15.2 to 17.7%. The experimental curd cheeses were characterised by water content consistent with the Polish Standard [23], its amount not changing significantly during storage [Table 3]. Moreover, the performed statistical analysis confirmed that the type of applied starter culture did not significantly affect, in general [except for the 3rd and the 7th storage day], the mean water content in the examined acid curd cheeses [Fig. 2, Table 2]. Like in case of water content, fat content fluctuations in the examined curd cheeses can be considered non-significant, basing on statistical analysis of the obtained results. The analysed curd cheeses A and B contained 10.86% and 11.82% fat, respectively, and the type of applied starter culture did have a clear-cut effect on its participation in the cheese mass.

The obtained results find their confirmation in the available references. In the study carried by Smietana et al. [31], aimed at assessing the quality of curd cheeses produced with the use of fully automated technological system, water content was found to range from 70.5% to 71.5%. However, no significant changes were stated in the chemical composition of tvarogs stored under cooling conditions. According to these authors, the success of the course of cheese production depends of how far maximum allowable water content happens to be maintained in respective cheese types, which is the same in the whole amount produced. Different content of water and fat in cheeses gives in consequence rise to receiving products with different organoleptic properties. On the other hand, a rise in the amount of leaven may result in the increase of water content in the finished products. The half-fat cheese produced by them was characterised by a firmer consistency [lower penetration degree] when compared to fat cheese. During the storage of half-fat cheese, an increase in consistency hardness was found, whereas in case of fat cheese no distinct changes of texture were observed. This is evidence of the stabilising role of fat in the shaping of curd cheese rheological properties during storage. The research of Żuraw et al. [37] showed that the type of applied leaven [DVS form and lyophilised REDI-SET form] did not have a clear-cut effect on water content in the cheeses examined by them. Small increase of water content during the storage of curd cheeses is explained by Cais and Wojciechowski [5] by a change in the temperature of cheese storage. This affects water migration outwards or inwards the cheese. The cooling [temperature below 8°C] gives rise to protein swelling and free water binding. Slightly higher water content affects favourably the taste and the aroma of curd cheese, thus becoming softer and more delicate [31]. The increased content of water is also reflected in the structure and the consistency of curd cheese, which become more plastic and homogenous, while its binding with the protein mass affects favourably the output and the increased economic efficiency. Pluta et al. [22] showed a drop in the water content during a three-week-long time of storing curd cheeses, both vacuum-packed [modified atmosphere packing] and non-vacuum-packed. The lowering of water content was induced by whey leakage and its accumulation within the packing. Smietana et al. [31] did not find an explicit reason for whey leakage during curd cheese storage. Natural method of protecting a product against syneresis may be application of lactic acid bacteria strains that produce mucous sheaths. In the study of Molska et al. [19], carried out on curd cheeses, slightly higher water content was found in the examined samples than that provided for in the standard. The recorded differences are explained by these authors by difficulties in setting up standard conditions of compressing with laboratory screw press.

In the analysed curd cheeses A and B, the initial hydroperoxide content amounted respectively to 0.479 and 0.442 mg malonic aldehyde per 1 kg cheese (Fig. 4). The statistical analysis of obtained results showed that the curd cheeses examined differed significantly [except for the 7th and the 35th storage day] in respect of hydroperoxide content and their amount in both cheese types did not significantly change during storage (Tables 2 and 3). However, no clear-cut effect was found of the applied starter culture on the content of secondary oxidation products in the experimental cheeses (Table 2). Moreover, mean content of that indicator in both curd cheese variants did not change significantly together as the storage time passed (Fig. 5, Table 3).

Fat oxidation secondary products, mostly aldehydes, can react with protein amine group producing complex compounds, which show anti-oxidative properties [34]. Important element that plays a part in milk fat auto-oxidation is phospholipids [36]. They may show anti-oxidative or pro-oxidative activity [10], however the mechanism of that activity of phospholipids has not been completely learned [9]. Furthermore, the interaction of protein and lipid fractions may affect the course of fat oxidation process. In interaction with protein, fatty acid hydroperoxides may give rise to oxidation of some amino [34]. According to the studies of Chen and Nawar [8], L-tryptophan, L-serine, L-tyrosine, L-lysine, L-histidine, L-alanine inhibits milk fat auto-oxidation. The main anti-oxidative role is performed by their alkine groups. The obstruction of these groups considerably decreases anti-oxidative properties of amino acids.

The performed statistical analysis of the mean content of conjugated diene structures in the analysed curd cheeses A and B showed the observed differences to be statistically non-significant in the whole storage time (Fig. 6, Table 2). Furthermore, the changes in mean conjugated diene content in both curd cheese types (with FLDAN and CHN-11 starter cultures) should be considered, basing on trend function analysis, as statistically non-significant (Table 3).

The content of conjugated trienes in lipids of curd cheeses A and B remained at a similar level in the whole storage time. Slight triene content increase in the fat of both cheeses on the 21st and the 28th day may result from a change in the dynamics of diene conversion into compounds of conjugated nature and from more intense conversion of triene structures into conjugated system between storage days 21 and 28 and on day 35 (Fig. 7). The estimated trend models confirmed that changes of conjugated triene structures in the whole storage time were statistically non-significant (Table 3).

The process of milk processing may affect linoleic acid oxidation with liberation of active radicals [36]. In addition, there is evidence that conjugated linoleic acid (CLA) may originate in result of free-radical peroxidation of linoleic and α-linoleic acids during technological process. The access of air facilitates CLA development through radical oxidation reactions. Whey protein may act as a proton donor, which may enable intensification of linoleic acid isomerisation process and generate enlargement of CLA participation in fat [1].

Oxidative transformations of polyenic fatty acids, of which hydroperoxides [16] and secondary oxidation products developed in result of auto-oxidation and due to further conversions, may give rise to formation of conjugated polyens [13]. Moreover, the presence of conjugated polyenic acids found in the present research might have been caused by the action of free radicals on the carbon chain with double and triple unsaturated bonds and by their natural occurrence in milk fat. It is It is stated that storage of dairy products, which contain large amount of CLA when compared with milk, does not affect changes in its concentration due to considerable stability of that component [36].

The performed examination showed, in general, a non-significant effect of the type of applied starter culture on the shaping of titratable acidity of the curd cheeses analysed. General drop was observed in the potential acidity of cheese A and a minimum increase of that indicator for cheese B (Fig. 8). However, basing of trend function analysis, the changes in titratable acidity of both curd cheeses should be considered as statistically non-significant (Table 3).

Like in case of changes in titratable acidity, the performed statistical analysis of obtained results confirmed, in general, the lack of significant differences in active acidity [pH] of the curd cheeses analysed. General pH increase in the cheese with FLDAN starter culture was observed and a drop of that indicator for the cheese with CHN-11 starter culture (Fig. 9). The changes in pH found in both curd cheese variants proved to be statistically non-significant (Table 3).

Important factor, influencing the changes in titratable acidity of low-fat and fat-rich curd cheeses in the first three storage days, according to Cais and Wojciechowski [5], is effect of temperature. After that time, a sudden drop occurs in the acidity, which may be explained by inhibition of lactic streptococci growth, and even by their partial dying out. The phenomenon described this way was not observed however in the samples analysed in the present study Bonczar et al. [3] reported a significant effect of the type of added leaven on the shaping of pH value of one-day cheeses made of goat milk. The changes in titratable acidity were also observed in experiments carried out by Molska et al. [19] on curd cheeses. During cheese storage, the acidity remained at the initial level, at least for 2 days, whereas its changes occurred in later time of storage.

The performed rheological analysis of experimental cheeses showed a significant effect of the applied starter culture on the hardness of curd cheeses examined, with its higher values being obtained by curd cheese A (FLDAN starter culture) in the whole study period. The hardness of curd cheese with FLDAN starter culture showed an increasing tendency in almost whole study period (except for the time between storage day 21 and 28). On the other hand, the course of changes for cheese with CHN-11 starter culture was more diverse (Fig. 10). The trend models determined for both variants of the analysed samples considerably differed against each other. In case of the curd cheese produced with the application of FLDAN starter culture, the increase of hardness was considered to be statistically significant, whereas the changes in hardness of the curd cheese produced with CHN-11 starter culture proved to be statistically non-significant.

Ziółkowski et al. [35], when examining the durability of curd cheeses produced according to modified production technology and packed with different methods (vacuum packing and thermo-shrinkable foil packing), found an increase in the hardness of all analysed samples during storage, which they explained by whey leakage. They also emphasised that the leakage was slight, and the differences in hardness were therefore minimum. According to Prentice [4], cheese rheorological properties depend mostly on their protein and water content. This author states that when protein content increases in cheeses, their hardness increase as well. The study performed by Bonczar and Walczycka [4] showed that water content was negatively correlated with almost all texture parameters, including hardness. This means that the smaller cheese water content, the higher hardness of this product.

The carried out research showed that the type of applied curd cheese starter inoculation affected mostly curd cheese organoleptic attributes and hardness. Therefore, attention should be paid to qualitative and quantitative composition of lactic acid fermentation bacteria, used in curd cheese production in the form of leavens, in order to receive a product of high taste and aroma values and characterised by appropriate consistency and structure.

CONCLUSIONS

1. Better taste and aroma attributes, larger hardness and lesser whey leakage were characteristic of the curd cheese produced using FLDAN starter inoculation.

2. Starter culture type did not significantly differentiate the produced curd cheeses in respect of fat and water content.

3. The acidity of cold-stored curd cheeses did not depend on the type of applied leaven.

4. The applied starter cultures affected the shaping of examined acid curd cheese hardness. Larger hardness in the whole study period was characteristic of the curd cheese produced using FLDAN starter culture.

5. During storage time, slower fat oxidation to primary and secondary products occurred in the curd cheese produced with addition of FLDAN starter culture than in that produced with addition of CHN-11 starter culture.

6. The applied starter cultures did not give rise to differences in the course of changes in conjugated fatty acid content (dienes and trienes) in both types of curd cheeses during storage at 5 °C.

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Accepted for print: 26.09.2007

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