MICROBIAL SPOILAGE MECHANISM OF DRIED/DEHYDRATED VEGETABLE PRODUCTS DUE TO HIGH WATER ACTIVITY DURING STORAGE

Singham Pragati*, Genitha T. R**., Birwal Preeti *M.Tech Food Process Engineering and Management, Department of Food Engineering, (NIFTEM, Haryana)

** Assistant Professor, Department of Food Process Engineering, (SHIATS, Allahabad) *pragati.niftem@gmail.com , **genitha@ahiats.edu.in

Table 1. Relation between drying method and microbial reduction for vegetables

Drying method Reduction in microbial count

Type of feed Examples

Tray 1.5 log Diced, sliced, chunks Pumpkin, carrot, tomato, garlic, onion, cauliflower, lettuce, ginger, celery, mushroom

Drum 2 log Puree, paste, slurry Potato, tomatoFluidized 2 log Whole(uniform), Peas, Freeze 3 log Sliced, diced, juices, Tomato, carrot, Spray 4.5 log Juices Tomato juice, carrot juice

Microwave-Augmented Freeze

Drying

3-4 log Diced, slices, paste, juices Tomato, peas, broccoli,

Ultrasonic 4.5 log Whole, sliced Onions, garlic

Explosion puffing 5.2 Chunks Mushroom

Refractance window 4-6 log Puree Tomato, sugarbeet,

Table 2. Water activity of selected vegetables (Okos et.al, 1992)

Dehydrated vegetables Moisture content (% d.b) aw Temperature (°C)

Potato 51015

0.120.470.69

36

Onion 51015

0.400.620.74

27

Celery 51015

0.430.590.69

25

Tomato 102030

0.440.610.69

27

Peas 5 0.25 25Dried vegetable mix 5 0.21 25

aw + 0.1 = Shelf life – 2x or 3x

Microbes ability to regain moisture i.e tolerance for low water activity

(Osmoregulation / Osmoadaptation)

Microbial invasion as a result of hygroscopic nature

Water migration from environment to cytoplasm via water channels

Maintenance of membrane turgor pressure

Establishment of internal equilibrium “Homeostasis”

Microbes start mutiplying i.e ceased lag phase become active