Hurdle technology involves simultaneous multiple preservation approaches, has generally helpful in controlling pathogens and maintaining food quality during storage [4]. The technology was applied to a bologna type sausage by lowering the pH, extending the heat treatment and reducing the amount of nitrite used. Positive hurdles, which keep the membrane lipids in apparently unchanged physiological condition and thus prolong the shelf-life of foods are: relatively low temperature, appropriate relative humidity, absence of light and slight anoxia. Another fundamental aspect of food preservation by hurdle technology is the synergistic effect of combined processes used  which causes disturbance of the homeostasis within microorganisms [5].Water activity of these products generally adjusted at less than 0.85 as Clostridium botulinum cannot grow and Staphylococcus species do not elaborate enterotoxin [6,7]. S. aureus are considered to be hazardous to the consumer, moreover it can grow even at an a_w as low as 0.83 and produce enterotoxin at aw values of 0.86 or higher [8].

HUMECTANTS AND ACIDULANTS

Karthikeyan et al. [16] developed Chevon (capine) keema, using the principle of hurdle technology. The hurdles applied were water activity (a_w), pH, vacuum packaging, preservatives and heat treatment. a_w of the product was adjusted to two levels viz., 0.90 and 0.88 by the addition of humectants. The pH of the keema was adjusted with lactic acid to 3 desired levels viz. 5.50, 5.65 and 5.80. Sensorically the product with pH 5.8 was the most acceptable and while pH 5.50 was the least acceptable. Standardised keema with aw 0.90 and pH 5.80 were stored at ambient temperature A gradual increase in moisture, a_w, TBARS number and tyrosine value were observed throughout the storage period. However, decrease in the growth rate of aerobic and anaerobic counts and complete inhibition of Staphylococcus aureus was observed. Product was well accepted up to the 3^rd day and fairly accepted up to 5^th day whereas the keema prepared by the traditional method was acceptable only on the first day.

Leistner [17] developed Lup Cheong (raw non-fermented sausage of China storable for several weeks without refrigeration) by the addition of 3.5% sodium lactate and 0.1% sodium acetate. The modified product remains tasty and is stable and safe even when stored for several weeks without refrigeration.

Lara et al. [18] prepared Charqui meats to observe the possibility of development of enterotoxigenic Staphylococcus aureus and Clostridium botulinum proteolytic type B spores and their toxins. Results demonstrated that the harsh processing conditions, high salt concentration, relative high temperature and water activity, inhibited the growth of both bacteria. C. botulinum spores germination also impaired might be because of the low aw conditions.

USE OF IRRADIATION AND COMBINATION ANTIMICROBIALS

Antimicrobial agents, including food preservatives have been used to inhibit food-borne bacteria and extend the shelf life of processed food. Antimicrobials in combination with other hurdles were being used to extend the shelf life as well as safety of hurdle treated products. The use of antimicrobials in combination is also referred to as multiple-hurdle technology [2,19,20].

Chawla and Chander [21] developed shelf stable meat products by using a combination of hurdles (irradiation, reduced water activity and vacuum packing) and effectiveness of these hurdle against Clostridium sporogenes, Staphylococcus aureus and Bacillus cereus were tested. Radiation treatment (2.5 kGy) resulted in complete elimination of S. aureus (inoculated 10⁶ cfu) and B. cereus but not of C. sporogenes. The water activity (a_w) of 0.85 and vacuum packaging of products prevented the growth of these organisms inoculated into these samples during 3 months of storage at room temperature. Irradiation usefully inactivated yeast and molds and reduced the B. cereus during storage.

Charqui meat is a tropical intermediate meat product formulated using hurdle technology [17]. Salt, sodium nitrite, dehydration, and packaging are hurdles sequentially applied to inhibit deteriorating microorganisms with the possibility of selecting desirable microbiota.

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