IMPROVEMENT OF NUTRITIONAL, HYGIENIC AND SENSORY PROPERTIES OF KAREISH CHEESE USING THYME AND BLACK SEEDS

Amany R. El-Bialy. The present study was aimed to improve nutritional, hygienic and sensory properties of kareish cheese by adding Thyme (Thymus vulgaris)andBlack seeds (Nigella sativa). According such aim, Kareish cheese was manufactured using fresh buffalo skim milk and starter cultures of Lactococcus lactis subsp. lactis and Lactococcus lactis subsp. Cremoris. Thyme andblack seeds were added with different concentrations of 1, 2 and 3%. Total phenolic content (TPC), free radical scavenging activity (RSA), antioxidant and antimicrobial activity as well as sensory evaluation were determined in Kareish cheese in fresh and during cold storage at 4±1 o C for 21 days. Results revealed that the kareish cheese supplemented with thyme or black seeds had high total TPC, RSA, ferric antioxidant power (FRAP). Concentration of 1 % thyme or black seeds was sufficient in respect to the slowing down of mould and yeast growth, but higher concentration, i.e. 3.0 % was showed more effective for inhibition of yeasts and moulds growth. This endowed potentiality can participate in keeping a good hygienic quality of kareish cheese during storage. Data showed the sample supplemented with 2% thyme or 3% back seeds had the highest flavor scores either fresh or during ripening. Data from present results concluded that thyme or black seeds can be used as an alternative natural preservative in the Kareish cheese, enhancing the nutritional value, hygienic quality and acceptable of taste .


Introduction
In developing countries, particularly in Egypt, low income people such as farmers, people in small isolated villages and native communities use Kareish cheese in their diet. Kareish cheese is one of the most popular types of soft cheese in Egypt, characterized by low fat content and an excellent dietary source of protein, calcium, phosphorous, and water-soluble vitamins (Aman, 1994; El Bagoury and Mosaad, 2002). However, it may be a vehicle for transmitting foodborne illness and causing food poisoning outbreaks due to contamination with different types of bacteria (El kholy et al., 1995).
Kareish cheese is a soft cheese commonly made and consumed in Egypt. Environmental conditions prevailing during storage, combined with the composition of the cheese often create possibilities for extensive development of mould on cheese surface, which reduces considerably its quality (Reps et al., 2002).
However, the food industry is now under pressure to reduce the use of synthetic antimicrobial chemical compounds, which appear to be experiencing a trend for 'green' consumerism and 'clean-labeling' of food products (Tajkarimi et al., 2010). As an alternative to synthetic preservatives, antimicrobial compounds from plants are becoming a positive selling point, thus creating a modern trend towards so-called 'natural' additives , preservatives and accepted by consumers (Burt, 2004).
Thyme herb (Thymus spp.) has various functions and medical uses. It is an antimicrobial, antifungal and has an antioxidant effects. Thus regular use of this herb improves the health and longevity of individual body cells and moreover the products fortified with it. Thyme herb contains many phenolic compounds and flavonoids such as glucuronide of apigenin, luteolin, eriodyctiol, luteolin glycosids, rosmarinic acid, quercitine Black seeds (Nigella sativa L.) or its oil is used as a diuretic, lactagogue and vermifuge (Ali and Blunden, 2003). The dried seeds from black cumin are also used for sprinkling on bread or flavoring foods, especially bakery products and cheese (Takruri and Daneh, 1998). Black seeds contain 36-38% fixed oils, proteins, alkaloids, saponins and 0.4-2.5% essential oil The present study was aimed to improve nutritional, hygienic and sensory properties of kareish cheese by adding thyme and black seed. According such aim, antioxidant and antimicrobial activity as well as sensory evaluation were determined in Kareish cheese prepared with adding different concentrations of thyme or black seeds in fresh and during cold storage at 4±1 o C for 21 days. Preparation of thyme and black seeds:-Thyme or black seeds were washed for any contaminates and crushed finely in mixer.

Materials and Methods:-
Manufacture and treatment of Kareish cheese:-Kareish cheese was manufactured according to the method adopted by Fahmi (1960) and prepared in Food Technology Research Institute, as follows: skim milk (0.5% fat and 8.75% SNF). Buffalo's skim milk was divided into seven equal portions. One batch had no herbs as a control. The second batches were fortified with thyme at the rate 1 to 3 % from milk weight for treatments T 1, T 2, T 3 . The latter batches were fortified with black seeds at the rate 1 to 3% from milk weight for treatments T 4, T 5, T 6 and well mixed with a blender. All the treatments were heated at 85 ºC for 15 Sec. and immediately cooled to 40ºC. Sodium chloride was then added to 1% concentration with stirring until completely dissolved and all the batches were inoculated with 2% starter culture containing about 10 8 cfu/ml at the rate of the weight of skim milk at 38°C with stirring well. The inoculated milk batches were incubated at 35°C overnight until curding. The formed curd was ladled into plastic frames lined with muslin cloth, dispersed on curd and then the curd pressed by suitable weights. Resultant cheeses were stored at 4 o C ±1ºC for 21 days. Analysis were taken from the finished cheese every 3 days up to 21 days. All treatments were of three replicates.

Determination of total phenolic content (TPC):-
Total phenolic content in kareish cheese samples was determined according to method of Zheng and Wang (2001) by using Folin-Ciocalteu reagent and the TPC was calculated by a standard curve prepared with gallic acid and expressed as milligrams of gallic acid equivalents GAE/100gm.

Determination of free radical scavenging activity (RSA) :-
The free radical scavenging activity (RSA%) in kareish cheese samples was measured using 2,2′-diphenyl-1picrylhydrazyl (DPPH) assay according to the method described by Brand-Williams et al. (1995). ) and expressed as percentage inhibition of the DPPH radical and was determined by the following equation: RSA% = Abs control -Abs sample x 100 Abs control Determination of Antioxidant activity :-Antioxidant activity was measured using the ferric antioxidant power (FRAP) assay of (Benzie and Strain, 1996).

Microbiological analysis:-
For examining the microbiological quality of kareish cheese, for each sample, 10g were weighed out and transferred to a sterile blender with 90 ml of 0.1% peptone and mixed thoroughly for 3 min to prepare the cheese homogenate.

Moulds and yeasts count in Kareish cheese during storage periods:-
The effect of adding different concentrations of thyme or black seeds on moulds and yeasts in Kareish cheese during storage periods at 4 o C for 21 days is presented in Table (4). The moulds and yeasts count detected in the control treatment (prepared without thyme or black seeds ) cheese was 2.26 log cfu/g and 4.22 log cfu/g of Kareish cheese after 6 days and after 21 days of storage respectively. The cheese prepared with thyme lead to the inhibition and retardation of moulds and yeasts growth and lowered the maximum growth levels in the cheese. The moulds and yeasts count ranged from the beginning 1.32 to 2.21 log cfu /g and 1.50 to 2.16 log cfu /g at the end of storage period in cheese samples prepared with 1% thyme or black seeds respectively, while the Kareish cheese samples prepared with 3.0% thyme or black seeds was not detected count. From the achieved results, it is clear that the addition of thyme or black seeds at concentration of 3.0% is relatively more effective than other concentration. These results are confirmed with ( Also, it was known that thymol and carvacrol, two major components of thyme , are both effective against E.coli and carvacol is more efficient (Fan and Chen, 2005). Also, the antimicrobial action of black seeds is originating from the phenolic compounds in black seeds which are considered as powerful active compounds expressing strong antimicrobial activities. From the results of the activities against pathogenic bacteria, it can be stated black seeds has general antibacterial activity against pathogenic bacteria. This endowed potentiality can participate in keeping a good hygienic a quality of cheese during storage under cold conditions (Ahn et al.,2004). Black seeds was characterized by high level of phenolics which are considered as powerful active compounds expressing strong antimicrobial activities (Luther et al., 2007). Table ( However, the counts of Lactococcus strains in kareish cheese with 3% of thyme (7.76 cfu/g) were higher than all treatment during storage . Over storage, counts of Lactococcus strains increased until 9 days in cheese controls, while the increase in thyme and black seeds fortified cheese were more pronounced until 15 days. These results explain thyme and black seeds improved viability of the Lactococcus strains during storage of kareish cheese. Shori (2013), study the 10 : 30% increase of viable cell counts (VCC) of Lactobacillus spp. and Streptococcus thermophilus, using soybean in cow-and camel-milk yogurt during refrigerated storage focuses on using additive such as soybean to improve the antioxidant and the viability of lactic acid bacteria .

Viable cell counts of Lactococcus spp:-
Sensory evaluation of the supplemented cheese during periods: -Sensory evaluation of Kareish cheese prepared with different concentrations of thyme or black seeds during storage periods at 5 o C for 21 days are presented in Table (5). Data showed the sample supplemented with 2% thyme or 3% back seeds had the highest flavor scores either fresh or during ripening. The flavor scores of 2% and 3% thyme or black seeds supplemented cheese after 21 days were 47 , 45, 44 and 47 respectively. However, continuous production of lactic acid and other organic acids lead to fragile cheese showing a gradual decrease in body and texture and appearance scores recorded for all cheese treatments up till the end of storage period. There were clear differences between control and cheese samples in appearance value.
Similar to appearance, the cheese supplemented with 2% thyme and 3% black seeds showed flavour scores very difference to control cheese. Furthermore, the cheese supplemented with thyme and black seeds ratio showed body and texture scores very close to control cheese. Body and texture results of the control, 2% thyme and 3% black seeds-supplemented cheese after 21 days of ripening were 36, 37 and 37 respectively. In all cheese treatments, the sensory evaluation scores gradually decreased during ripening period. Also, it was clear that addition of 2% thyme or 3% black seeds produced Kareish cheese with high sensory acceptability than the control both fresh and stored in the refrigerator for 21 days. These results are in agreement with those obtained by Foda et al. (2008).

Coskun et al. (1996):-
reported that cheeses with lower concentration (1 and 2%) herb were mostly preferred by the panelists in term of total score than higher herb concentration (4 or 5%). On the other hand, both descriptive and hedonic evaluation presented same results.