PALLVI DHOTRA ROLL No. 06FOOD SCIENCE & TECHNOLOGY
Hurdle technology is the combined use of several shelf-preservation methods to make a product shelf-stable,to improve quality and to provide additional safety.Also known as “combined method technology”.Leistner in 1976, introduced the term “hurdle effect”.NEED FOR HURDLE TECHNOLOGYConsumers are demanding for fresh, natural andminimally processed food products.Ongoing trend has been eat out and to consume readyto eat foods.New ecology routes for microbial growth have emerged. emerged.
Preservative factors or hurdles disturb thehomeostasis of microorganisms.Microorganisms should not be able to “jump over”all the hurdles present in the food product.Preservative factors prevents microorganisms frommultiplying and causing them to remain inactive oreven die.The hurdle concept illustrates that complexinteractions of temperature, water activity, pH etcare significant to the microbial stability.
High Temperaturei. Pasteurization mild heat treatment (e.g., 63oC for 30 min; 100oC for 12 sec) high product quality destroys vegetative pathogens (disease-causing microbes) (disease- shelf- reduces total microbial load, increases shelf-life does not destroy spores (dormant stage of some bacteria) usually combined with other hurdles (e.g., refrigeration)
ii. Sterilization complete destruction of microorganisms severe heat treatment (equivalent to several min at 121.1oC) destroys spores gives "shelf-stable" product "shelf- some nutrient, quality destruction (colour, flavour, texture)
iii. Blanching blanching is a kind of pasteurization generally applied to fruits and vegetables primarily applied to inactivate natural enzymes commonly practiced when food is to be frozen depending on its severity, also destroys microorganisms
Vegetative cells, as well as, viruses are 60° 80°destroyed at temperature 60°C to 80°CHigher temperature may be needed forkilling of thermophilic microorganismsVegetative cells are killed in 10 minutes at100°100°C and many spores in 30 minutes at100°C100°
Low Temperaturei. Refrigeration ideally 0oC to 4oC for most foods short- short-term preservation (days to weeks) high product quality (fresh, minimally processed, sous vide) slows down microbial growth, respiration, enzyme/chemical reactions some pathogens can grow (e.g., C. botulinum (type E), Listeria)
ii. Freezing generally -18oC to -30oC quality depends on product, time, temperature long- long-term preservation (months to years) stops microbial growth, respiration slows down chemical reactions must have good packaging
Reduced Water Activity (aw) aw is water "availability" water is required for microbial growth, enzyme/chemical reactions pathogenic microorganisms cannot grow at aw < 0.86 yeast & moulds cannot grow at aw <0.62 free water can be removed by concentration, dehydration and freeze drying in general, the lower the aw, the longer the storage life
Increased Acidity (lowered pH) acidity slows down growth of spoilage organisms and pathogens pathogens wont grow, spores wont germinate at pH<4.5 (e.g., fruit juices, sauerkraut) above pH 4.5, must sterilize for shelf stability below pH 4.5, can pasteurize
Controlling Oxygen low oxygen inhibits growth of many spoilage organismsbut: anaerobic conditions required by some pathogens (e.g., C. botulinum)Preservatives inhibit bacteria, yeasts, moulds used at low levels (mg/kg) for specific applications e.g., benzoate (soft drinks), propionate (baked goods), nitrites (meats), sulfites (wine), ascorbate (juices)
Sulphur dioxide and SulphitesNitrites and NitratesSorbatesPropionatesSodium benzoate
Sequence of hurdles ensures stability at eachstage. All hurdles decline with time except aw.Nitrite inhibits pathogensgrowth of other bacteria depletes oxygen acid-Low oxygen favours acid-producingcompetitive floraAcid decreases pHAw hurdle gradually increases due to drying.
These products have pH > 4.5 and aw > 0.85.Should have to comply with the low-acid low-canned food regulations (i.e., commercialsterilization).However, for quality reasons, these productscannot be given a sterilization process.Instead, the spreads are stabilized by moderatelevels of salt, decreased pH and moisture.
Improves product quality and microbial safety.Save Money, Energy & Several other Resources.Foods remains stable & safe, high in sensory &nutritive value due to gentle process applied.Doesnt effects the integrity of food pieces (fruits).Applicable in both Large & Small Industries.Manufacture of new products according to the needof processors and consumers.
BOOKS-BOOKS- A text book of food preservation - BY NEELAM KHETARPAL. Food microbiology - BY Food science – BYWEBSITES-WEBSITES-<http://www.ifrn.bbsrc.ac.uk/safety/comicro /Culture_25.pdf><http://ars.usda.gov/Services/docs.htm?doci d=6786