EFFECTS OF SODIUM BICARBONATE ON MILK PRESERVATION

Chemical properties The present investigation was carried out to assess the effect of sodium bicarbonate (NaHCO3) on the keeping quality of raw cow milk. Milk samples were collected from Bangladesh Agricultural University (BAU) Dairy Farm and initial quality were evaluated using physical and chemical tests at Dairy Technology Laboratory of the Department of Dairy Science, BAU. Then, collected samples were preserved at room temperature (2830°C) with 0.0 (control), 0.3, 0.4 and 0.5 per cent NaCHO3. The quality of milk samples were measured at every two hours interval up to 6 hours, one hour interval upto 16 hours and thereafter every half an hour interval until spoilage. Initially, colour, flavour and texture of all milk samples were normal (100%), but with progressive storage time colour, flavour and texture of all samples deteriorated gradually, which was more rapid for control samples than that of the NaHCO3 treated samples. Acidity per cent of all samples increased gradually during storage period and the differences in acidity of milk samples in different treatments were significant (p<0.01). Control samples spoiled after 111⁄4 hours but that of 0.3, 0.4 and 0.5 percent NaHCO3 treated samples spoiled after 163⁄4, 173⁄4 and 183⁄4 hours,, respectively. It may be concluded that NaHCO3 is the effective chemical neutralizing the acids produced by acid producing bacteria and can be used as a short term preservation of milk under rural condition of Bangladesh where scientific cooling or pasteurization facilities are not available.

The present investigation was carried out to assess the effect of sodium bicarbonate (NaHCO3) on the keeping quality of raw cow milk.Milk samples were collected from Bangladesh Agricultural University (BAU) Dairy Farm and initial quality were evaluated using physical and chemical tests at Dairy Technology Laboratory of the Department of Dairy Science, BAU.Then, collected samples were preserved at room temperature (28-30°C) with 0.0 (control), 0.3, 0.4 and 0.5 per cent NaCHO3.The quality of milk samples were measured at every two hours interval up to 6 hours, one hour interval upto 16 hours and thereafter every half an hour interval until spoilage.Initially, colour, flavour and texture of all milk samples were normal (100%), but with progressive storage time colour, flavour and texture of all samples deteriorated gradually, which was more rapid for control samples than that of the NaHCO3 treated samples.Acidity per cent of all samples increased gradually during storage period and the differences in acidity of milk samples in different treatments were significant (p<0.01).Control samples spoiled after 11¼ th hours but that of 0.3, 0.4 and 0.5 percent NaHCO3 treated samples spoiled after 16¾ th , 17¾ th and 18¾ th hours,, respectively.It may be concluded that NaHCO3 is the effective chemical neutralizing the acids produced by acid producing bacteria and can be used as a short term preservation of milk under rural condition of Bangladesh where scientific cooling or pasteurization facilities are not available.

INTRODUCTION
Milk is the nature's almost perfect food.According to Eckles et al. (1971) milk contains on an aver average 87.25% water and 3.80% fat, 3.50% protein, 4.80% of lactose and 0.65% minerals.Besides these milk contains considerable amount of fat soluble vitamins (Vit.A, D, E, K) and water soluble vitamins (Vit.Bcomplex and Vit.C).The nutritive value of milk depends on its freshness, cleanliness, purity and wholesomeness.For this reason, the time interval between milk collected from the small farmers to the consumers is primarily most important.There is every possibility of spoilage of milk during that time.So, it is very important to adopt some technique for increasing the shelf life of milk.The presence of different types of microorganisms or undesirable bacteria in milk may cause deterioration of flavour, colour, taste or physical appearance.At the same time spoilage takes place rapidly due to the formation of excess lactic acid from the breakdown of lactose by lactic acid producing bacteria.To make the milk safe for public health and also to increase its shelf life it is very important to preserve milk scientifically.Due to lack of proper milk preservation facilities, a huge quantity of milk undergoes spoilage every year in our country.
Milk can be preserved for a while for human consumption by using some chemical substances such as hydrogen peroxide (H2O2) (Hossain et al., 1989), sodium bicarbonate (NaHCO3) (Kukde et al., 1991), etc. and by regulating the temperature i.e. cooling, pasteurization and boiling.Cooling and pasteurization facilities are not available throughout the country.At the same time, heated boiled milk is not also popular in our country.Established dairy farms have modern facilities for milk preservation but small farmers or the poor formers or vendors or goalas who live in rural areas have no such types of facilities for milk preservation.Most of the farmers or vendors are illiterate and they do not know how to preserve milk scientifically.It is urgently needed to develop low cost short time milk preservation technology in order to reduce the spoilage of milk which usually occurs during transportation and keeping long time without applying any scientific technique before marketing.
Sodium bicarbonate (NaHCO3) is a cheap chemical available in local market, present in powder form, white in colour and very easy to handle.Haddadin et al. (1996) from a preliminary study found that sodium bicarbonate is useful for short time preservation of milk.It is expected that handling of this chemical will be very easy by the farmers and there will be no hazards effects on public health.Local goalas or vendors or farmers are using this chemical for milk preservation but scientifically its feasibility as milk preservative has not been carried out widely.Hence, this experiment was conducted to monitor the usefulness of sodium bicarbonate (NaHCO3) as milk preservative.

Site of experiment
The experiment was conducted at Dairy Technology and Dairy Microbiology laboratory of the Department of Dairy Science, Bangladesh Agricultural University (BAU), Mymensingh-2202, Bangladesh.

Sources of milk
Whole milk was collected from, BAU Dairy Farm, Mymensingh-2202, Bangladesh.Suggestions were given to the milkers before milking the cows for maintaining all hygienic measures.Milk was poured from one pail to another after milking.To avoid the incorporation of air it was allowed to stand for a while and thereafter milk was taken to the Laboratory for experimental purpose.

Experimental procedure
The collected milk samples after thoroughly mixing was divided into four equal parts.Out of four parts, one was kept as whole milk without NaHCO3 (control) and the other three parts were preserved with different levels of NaHCO3 such as milk sample with 0.3% NaHCO3; milk sample with 0.4% and milk sample with 0.5% NaHCO3.
The physical, chemical and microbiological parameters used to monitor the qualities of milk were determined initially just before adding NaHCO3 and then after two hours interval upto 6 hours, one hour interval upto 16 hours and thereafter every half an hour interval until the milk samples were spoiled.

Physical and chemical tests
The physical and chemical tests of each milk sample were performed in the laboratory.The physical test comprised of organoleptic tests, viz., colour, flavor and texture, specific gravity, clot-in-boiling and stability using alcohol test of milk.The chemical test included the acidity test only.Organoleptic tests were performed with an expert panel of judges.Specific gravity, clot-on-boiling and alcohol test was done as per method described by Tessama and Tibbo (2009).Acidity test was done by titrating milk with N/10 NaOH solution as per method described by Bilkis et al. (2013).

Statistical analysis
Statistical analysis was done by using Randomized Complete Block Design (RCBD) as per Bailey (2008).Analysis of variance was done to find the statistical difference (Significant or not) among the different treatments and in case of significant difference LSD value was calculated to make a comparison among the treatment means.

Initial quality of milk
The physical, chemical and microbiological qualities of milk were determined before adding NaHCO3 with milk sample.Results obtained from initial analysis were in the standard level and are presented in Table 1.

Colour
Colour of all milk samples before starting experiment was normal (golden yellowish white).No abnormality in colour was detected (Table 1).Regarding milk colour, Eckles et al. (1971) stated that milk ranges in colour from a bluish-white to a golden yellowish, depending upon the breed of animal, the kind of feed and the amount of fat and solids present.In large qualities, milk appears entirely opaque while in thin layers, it is slightly transparent.Milk from which the fat has been removed or milk which is low in fat percentage shows a bluish tint.
From the Table 2, it is evident that for whole milk (control) and 0.3, 0.4 and 0.5 percent NaHCO3 treated milk samples, color was normal upto 10½ th , 16 th , 17 th and 18 th hours, respectively and after which color became bleached.Colour deterioration was very rapid in whole milk (control) followed by 0.3, 0.4 and 0.5 percent NaHCO3 treated milk samples.This indicates that NaHCO3 could be used as a short term milk preservative under rural areas where scientific cooling or pasteurization facilities are not available.

Flavour
The flavour of all milk samples before starting the experiment was normal (100%).All samples showed pleasing aromatic flavour.It has been shown that the pleasing aromatic flavour of milk may be correlated with high lactose and relatively low chloride content.Low lactose and high chloride content probably would mean milk with salty flavour (Eckles et al., 1971).Biswas (1997) found that flavour of all milk samples collected from BAU dairy farm was normal.In this experiment, flavour of whole milk (control) and 0.3, 0.4, and 0.5 percent NaHCO3 treated milk samples were acceptable upto 11¼ th , 16½ th , 17½ th and above 18¾ th hours, respectively (Table 3).After that time, the flavour was becoming unacceptable.This result showed that NaHCO3 is effective for controlling the flavour of milk.This was due to the fact that in fresh milk (control) lactic acid produced from the fermentation of lactose was not neutralized.But in NaHCO3 treated milk samples lactic acid produced was neutralized by NaHCO3 and hence the keeping quality of milk was increased.

Texture
All milk samples before starting the experiment was normal in Texture.The texture of all milk samples is shown in Table 4. Texture of normal milk is designated as free flowing liquid.Its viscosity is higher than water.Some solids exits in true solution phase, some are at colloidal state and some other portions as coarse dispersion phase.Texture of milk changes if some portion of fat is removed or water is added for adulteration purpose.In such case, milk becomes less viscous.Acidity development can also change the texture of milk.So the present results indicate that milk collected from BAU Dairy Farm was fresh and no fat had been removed from the milk.The normal texture of milk is stated as "free flowing liquid".From the Table 4, it is evident that the texture of whole milk (control) and 0.3, 0.4, and 0.5 percent NaHCO3 treated milk samples were normal upto 10½ th , 16 th , 17½ th and above 18¾ th hours of study, respectively.Thereafter samples become clotted.The whole milk (control) sample clotted earlier than NaHCO3 treated milk samples.The clotting time depends upon the percent of NaHCO3 used for preserving milk.Texture deterioration was rapid in fresh milk due to lactic acid production than treated milk with NaHCO3.

Specific gravity
Average specific gravity of milk samples was 1.031±0.0016.The specific gravity was within the normal range of specific gravity of milk.Generally the specific gravity of fresh milk is within the range of 1.027 to 1.035 having an average value of 1.031 (Eckles et al., 1971).Adulteration of milk by adding water decreased its specific gravity.In our experiment, the average specific gravity of milk samples was within the normal range but slightly below the average specific gravity of milk (1.031).This might be due to high fat and slightly low SNF content of milk.Eckles et al. (1971) stated that as milk fat is the lightest constituents of milk, the more that is present, lower the specific gravity will be and in a like manner, the greater the percentage of SNF the heavier the milk will be.Similar type of specific gravity was obtained by Biswas (1997) for BAU Dairy Farm milk.

Clot-on-boiling test (COB)
The results of acidity tests were confirmed by clot-on-boiling (COB) test.The test showed negative results indicated that there was no developed acidity and the quality of the milk sample was good.The results of COB test are shown in (Table 5).The COB test was positive at 11½ th , 16¾ th , 17¾ th and 18¾ th hours for whole milk (control) and 0.3, 0.4 and 0.5 percent NaHCO3 treated milk samples, respectively.From this result, it is clear that whole milk (control) sample clotted earlier than that of NaHCO3 treated milk samples.This was due to more acid production in fresh milk samples.On the other hand, NaHCO3 neutralized the acids produced by lactic acid producing bacteria from the breakdown of lactose.Clot-on-boiling test confirms the results of acidity test.This test also indicates that NaHCO3 could be used as milk preservative under village or rural areas of Bangladesh.The result of this study agrees with the results of El-Safety et al. (1978), Hossain (1989) and Barabas (1995).

Acidity test
Results of acidity test are shown in Table 7. Mean initial acidity of experimental samples was 0.1173±0.49.Generally acidity of normal milk samples are within the range of 0.10 to 0.20 (Eekles el al., 1971).Similar types of acidity (0.13%) were reported by Biswas (1997) for BAU Dairy Farm milk.Acidity test of milk is a good indicator of milk quality.Fresh milk shows an acidity of about 0.12% which is due to the presence of citrate, phosphate, carbon-dioxide and milk casein.If the milk samples is kept for several hours without

Table 1 .
Observation of the quality of milk before adding the preservative *Initial quality of milk before starting the experiment

Table 2 .
Colour quality of control and different proportions of sodium bicarbonate treated milk samples during

Table 3 .
Flavour quality of control and different proportions of sodium bicarbonate treated milk samples during

Table 4 .
Texture quality of control and different proportions of sodium bicarbonate treated milk samples during

Table 7 .
Average acidity of control and different proportions of sodium bicarbonate treated milk samples during preservation period