Effect of Water Activity on the Physico-chemical, Microbiological and Sensory Qualities of Buffalo Meat Sausage Stored under Ambient Temperature
S. Sureshkumar ,
V. Venkataramanujam ,
The study was undertaken to find the effect of water activity on buffalo sausage quality and storage stability at ambient temperature. Water activity (aw), temperature and pH have been identified as the three primary factors controlling microbial growth. The water activity of the buffalo meat sausage (treated) was adjusted to 0.88 by addition of humectants viz., salt, sugar, ISP, HVP, sodium lactate and subsequent heat treatment while the aw of the untreated sausage was 0.932. Tyrosine value showed a significant increase throughout the storage periods. There was a marked but not significant decrease in the TBARS number of the treated samples. On 5th day, the TBARS value of the treated sausages exceeded the threshold limit of 2 mg kg-1 resulting in the spoilage. The treatment had a significant inhibitory effect on the TVC, Staphylococcal count and Streptococcal count and anaerobic count. Whereas in case of coliform and yeast mould count it had no significant effect. On the third day of storage the flavour and texture, juiciness and over acceptability scores were well within the acceptable range. Whereas in the case of untreated samples there was a slime formation and off odour development on the 3rd day of storage. Although the sensory score (over all acceptability) of the treated samples were scored less (p>0.05), the product was acceptable upto 3rd day storage whereas the untreated samples spoiled after 1st day of storage.
to cite this article:
S. Sureshkumar , V. Venkataramanujam , K. Dushyanthan and A. Kalaikannan , 2006. Effect of Water Activity on the Physico-chemical, Microbiological and Sensory Qualities of Buffalo Meat Sausage Stored under Ambient Temperature. American Journal of Food Technology, 1: 166-172.
Most of the meat produced in India is being sold in the form of fresh meat,
only less than 3% is being sold as processed meat. Because of the rapid urbanization
and hurried way of life, there is a spurt in the consumption of processed foods
and a shift in the consumption pattern. Buffalo meat being comparatively cheaper,
will have additional advantages over other meats. Sausage is a popular and highly
relished meat product world over. The present low level processing of meat is
mainly because of the difficulties in marketing by maintaining the cold chain
of the products. To overcome this problem a technology has to be developed to
store the meat products under ambient temperature without recourse to refrigeration.
Hurdle technology (also called combined methods, combined processes, combination
preservation, combination techniques or barrier technology) advocates the deliberate
combination of existing and novel preservation techniques in order to establish
a series of preservative factors (hurdles) that present should not be able to
overcome by any microorganisms. These hurdles may be temperature, water activity
(aw), pH, preservatives and so on (Leistner and Gorris, 1995). Water
activity (aw), temperature and pH have been identified as the three
primary factors controlling microbial growth in many foods. However, most investigators
have not directly considered aw. Instead, they have modeled the effect of sodium
chloride concentration, the humectants used to modify aw (McMeekin
et al., 1987). Even though there are several studies on Intermediate
Moisture Foods (IMFs), relatively scant information is available on the Hurdle
Technology Foods (HTFs). Recently, the storage life of tandoori chicken with
aw 0.86 and pH 5.3 was extended to 2 days (Manish Kumar and Berwal,
1996) by the application of hurdle technology. The present study was undertaken
to investigate the effect of this important hurdle (water activity-aw)
on the physico-chemical, microbiological and sensory qualities of the buffalo
meat sausage stored under ambient temperatures.
Materials and Methods
Hot boned meat and fat from buffalo carcasses were collected from local corporation slaughter house, Chennai and were cleaned with potable water. They were chilled for 24 h at 4±1°C and then frozen to -18±1°C. On the day of experiment the frozen meat was thawed before being minced through a 4.5 mm plate of a meat mincer (OMAS, Model No. 169789, Electrolux food service, Italy).
Preparation of Buffalo Meat Sausage
The minced meat and fat were chopped in bowl chopper (Model MTK 662, Maschinen
fabrik., Germany). The emulsion was prepared by adding minced meat and other
ingredients of recipe (Table 1). The specified quantities
of salt, sodium tri polyphosphate and sodium nitrite were premixed and added
to the meat mix. The refined vegetable oil (sunflower) was cooled to 4°C
before adding to the mixture. During chopping the temperature of the emulsion
was maintained at 10-12°C by the addition of slushed ice. The emulsion was
then stuffed into 18-20 mm diameter sheep casing using a sausage stuffer (Model
MWF 591, Maschinen fabric., Germany), linked and cooked in hot air oven at about
100°C for 60 min so as to reach the internal core temperature of 72°C.
The cooked sausages were vacuum packed in multilayer (Polyester/Polyethylene
pouches of size 6"x 9") pouches to prevent post processing contamination. The
vacuum packaged sausages were served warm to taste panelists on day zero and
subjected to storage studies.
Trial for Optimum Level of Humectants
Different levels of humectants viz., sugar (1 and 2%); Isolated Soya Protein
(ISP) (Supro 500-E1, Protein Technologies International, St. Louis, 3 and 5%),
whole egg powder (SKM Foods, India, 1, 2 and 3%), hydrolysed vegetable protein
(HVP) (Protchem India, 1 and 2 %) and sodium lactate (Lactochem, Chennai, 2
and 3%) were tried. Incorporation of sugar beyond 1% resulted in an undesirable
sweet taste to the product. The product with ISP at 5% level resulted in the
soya flavour masking the meat flavour, the optimum being at 3%. The whole egg
powder at 1% was found to be optimum with good sensory qualities. Preliminary
trials revealed that the HVP at 2% render a salty taste and 1% was found to
be optimum. Sodium lactate at 3% level resulted in a sour taste and 2% level
was found to be optimum. The levels of ingredients including preservatives used
in the control and treated formulations are presented in Table
Measurement of Water Activity (aw)
The aw of the sausage sample was determined by a slight modification
of the procedure recommended by Lerici et al. (1983). An approximately
50 g sample was packed in a 60 mL glass tube and the mouth was corked air tight.
|| Formulation of sausage
|Added on meat and fat basis
Then it was immersed in a cooling chamber which had precooled ethanol at -30°C
to -35°C in a glass beaker and kept in a deep freezer (Vertical type, Vest
Frost, Denmark). A resistance thermometer probe was introduced inside the cork
to monitor the temperature. The rate of decrease in temperature was observed
which was constant up to a specific point and thereafter, the rate markedly
decreased. The point, where the rate altered was indicated by the start of ice
crystal formation, was taken as the freezing point of the sample. The freezing
point was converted to water activity value using the formula developed by Lerici
et al. (1983).
where ln is the natural logarithm, T is freezing point temperature in Kelvin.
Effect of Water Activity (aw) on the Product Quality
and Storage Stability
The buffalo meat sausage with water activity (aw) 0.88 was achieved
by the addition of humectants and by subsequent over cooking. The sausage prepared
without humectants served as control. The data obtained from six trials were
analysed. The products were stored at ambient temperature (35±2°C)
and analysed for the following quality attributes; pH, tyrosine values (Strange
et al., 1977), thiobarbituric acid reactive substances (TBARS) (Tarladgis
et al., 1976), moisture (APHA, 1976) and water activity. Total viable
count, coliform count, staphylococcal count, streptococcal count, yeast and
mould count and anaerobic count were enumerated (APHA, 1984). Sensory attributes
were evaluated by semi-trained panelists using the 9 point hedonic scale. The
results obtained from the above experiments were statistically analysed (Snedecor
and Cochran, 1989).
Results and Discussion
Table 2 shows that the pH of the untreated samples were
significantly (p<0.01) lower (6.36±0.03) than the treated samples
(6.44±0.02). This may be due to the addition of HVP, ISP and sodium lactate,
which was appreciated in the 0 day samples. This was in agreement with Karthikeyan
et al. (2000). The addition of humectants like sugar, HVP, ISP and sodium
lactate significantly (p<0.01) reduced the product water activity (0.884±0.001).
Upon storage at ambient temperatures, the aw showed a significant
(p<0.01) linear increase which was in agreement with Prabhakar and Ramamurthi
(1990). The moisture content of the treated samples were significantly (p<0.01)
lower (47.50±0.45) than the untreated samples (60.85±0.56). The
moisture content of all the samples were significantly (p<0.01) increased
from 52.17±1.96 on day 0 to 57.28±1.98 on day 5.
|| Effect of aw of physico-chemical properties of
buffalo meat sausage
|Means bearing same superscripts do not differ significantly
Similar changes in the aw and moisture were also observed in intermediate moisture deep fried mackerel (Che Man et al., 1995) and Sudanese dry meat (Gailani and Fung, 1989). The tyrosine value of the treated samples were significantly (p<0.01) higher (22.77±2.39) over the untreated (15.68±2.17) samples ( Table 2). This may be due to the denaturation and subsequent proteolysis of ISP during heating which was accentuated by addition of lactic acid (Syed et al., 1995). Throughout the storage periods the TV showed a significant (p<0.01) increase in all the samples which may be due to the protein breakdown by chemical and microbial actions. Karthikeyan et al. (2000) also observed higher protein degradation during storage in caprine keema at ambient temperatures. There was a marked but not significant decrease in the TBARS number of the treated samples conversely Karthikeyan et al. (2000) found a significantly higher TBARS number of hurdle treated caprine keema. This may be due to variation in production presentation, comminuted non-emulsion product, which may facilitate the fat oxidation. Upon storage, all the samples showed a significant increase in the TBARS number whereas between 0 and 1 day of storage the differences were not significant. In the treated samples the TBARS number were slightly decreased from 0 and 1st day of storage. The decrease in the TBARS number upon storage was in agreement with Kalaikannan et al., (2005). The TBARS values of sausage beyond the threshold limit of 2 mg kg-1 (Watts, 1962) on 3rd and 5th day for untreated and treated sausage, respectively, which may be due to increase in oxidation upon storage.
The TVC of the treated samples were significantly (p<0.01) lower than
the untreated samples (Table 3). Upon storage, the untreated
samples exceeded (log 7.65±0.40) the spoilage limit of log 7 (Hytiaineu
et al., 1975) on 5th day of storage while in the treated samples, the
TVC was well within the acceptable limit. Irrespective of the treatment, all
the samples showed a steady increase in the TVC during storage periods. Sahoo
and Anjaneyulu (1997) also observed a gradual increase in TVC of the buffalo
meat nuggets during the storage periods. There was no marked difference between
the treatments on the coliforms count, whereas during the storage periods, it
it showed a significant (p<0.01) increase from log 0.17±0.11 on day
0 to 2.11±0.04 on day 5.
|| Effect of aw on the microbiological qualities
of buffalo meat sausage
|Means bearing same superscripts do not differ significantly
The treated samples had a significant (p<0.01) lower staphylococcal
and streptococcal counts. Althought the soya protein tends to increase
the microbial load (Chowdhury et al., 1994), the reduced aw
lowered the microbial growth (Karthikeyan et al., 2000) in treated samples.
The staphylococcal and streptococcal counts showed a significant (p<0.01)
increase during the storage periods. A logarithmic increase in TVC and gradual
increase in staphylococcal count of the untreated sausage might be due to the
conducive aw (Leistner et al., 1981). The was no significant
difference between the treated and untreated samples in the yeast and mould
count. The yeast and mould counts were significantly (p<0.01) increased over
the storage periods irrespective of all treatments. The anaerobic counts of
treated sausage samples were significantly (p<0.01) lower than the untreated
sausage samples. In the present study, both the samples were vacuum packed which
might have facilitated the growth of anaerobic organisms. Fu et al. (1992)
also reported that the anaerobes and facultative anaerobes are the most important
spoilage bacteria in vacuum packaged meats. In case of treated samples, the
reduction in the aw might be attributed to the destruction of vegetative
cells (Leistner and Gorris, 1995). Hence the overall reduced level might be
noticed in the anaerobic counts of the treated samples.
Both the treated and untreated samples were spoiled on 5th day, hence only
the appearance scores were recorded (Table 4). Upto 3rd day
of storage, the appearance scores for both the samples were highly acceptable
whereas it was moderately acceptable on 5th day. This may be due to the slime
formation and discoloration due to microbial activity. In the treated samples,
the flavor scores were well with in the acceptable range upto 3rd day of storage
whereas in case of untreated samples it was only upto 1st day of storage. A
sudden decrease in the flavor scores for untreated samples on the 3rd day and
subsequent spoilage might be due to increased liberation of fatty acids and
oxidation of fat (Santamaria et al., 1992). Due to the development of
off flavor and slime formation in the untreated samples on the 3rd day of storage
the texture, juiciness and overall acceptability scores were not recorded. The
treated sausage samples were scored lesser than the untreated samples for texture,
This might be due to the adition of humectants which imparts the rubberiness
to the product.
|| Effect of aw on the sensory qualities* of buffalo
|* 9 point hedonic scale. Means bearing same superscripts do
not differ significantly
The juiciness score of the treated samples were lesser than the untreated samples
which may be due to the reduction in the moisture content. Even though there
was a decrease in the juiciness score, the difference were not significant.
There was no significant difference between the treatments in the overall acceptability
scores because the overall acceptability scores of the untreated samples were
not recorded after one day of storage. Incase of treated samples the overall
acceptability scores were 7.39±0.24. Upon storage, all the sensory scores
showed a significant (p<0.01) decrease. Based on the sensory quality studies
the treated samples were acceptable upto 3rd of storage whereas in case of untreated
samples it was only upto 1 day of storage.
The water activity was adjusted by employing the humectants viz., salt, sugar, ISP, HVP, sodium lactate and subsequent heat treatment. The product was acceptable upto 3rd day storage whereas the untreated samples spoiled after 1st day of storage. Further extension of the shelf life of the sausage can be explored by the use of antioxidants in the formulation in order to prevent the rapid lipid oxidation.
The author is grateful to the Director, CSWRI and ICAR for granting him the study leave to undergo Ph.D programme. The author also expresses his gratitude to the Dean, Madras Veterinary College for providing facilities to carry out the research work. He thanks M/s. Protein Technologies Inc., Protchem India and M/s.SKM Foods, India for the supply of Isolated Soy Protein, Sodium lactate and whole egg powder respectively.
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