SPOILAGE OF VEGETABLES

BY DAKSHITA NAITHANI

INTRODUCTION

Vegetables are an important element of the diet since they include a variety of essential nutrients such as carbohydrates, minerals, vitamins, roughage, and so on. Microbial deterioration causes around 20% of vegetables produced for human use to be wasted.

Spoilage is defined as any alteration in food that renders it unfit for human consumption.

REASONS FOR SPOILAGE

Vegetables, because of their high nutritional content, can promote the growth of moulds, yeasts, and bacteria, and thus can be ruined by any or all of these microorganisms. The presence of more water in vegetables encourages the growth of spoilage bacteria, and the low carbohydrate and fat content implies that much of this water is in useful form. Furthermore, vegetables’ tissues have a higher pH than fruits, making them more sensitive to bacterial invitation.

Vegetables’ relatively have strong oxidation-reduction potential and lack of significant poising capacity which indicates that aerobic and facultative anaerobic types are more essential than anaerobes.

In terms of frozen vegetable products, the total numbers of bacteria on frozen vegetables tend to be lower than on non- frozen products. This occurs primarily due to:

  • Blanching of products prior to freezing them.
  • Selection of higher quality products for freezing.
  • Some bacteria dying in the frozen state.

HOW DO MICROBES INVADE VEGETABLES?

Vegetables being a part of fresh produce contain high moisture which makes them highly perishable and hence more prone to spoilage.

Microbes gain entry into vegetables from various sources. These include:

  1. Soil
  2. Water
  3. Diseased plant
  4. Harvesting and processing equipments
  5. Handlers
  6. Packaging and packing material
  7. Contact with spoiled vegetables
  8. Freshly picked vegetables contain a natural surface flora, which includes pectinolytic bacteria in low quantities. The plant’s intact healthy tissue may also include a small number of live bacteria. The interplay between physiological changes in the tissues after harvest and changes in microbial activity will determine the start and pace of deterioration. The act of harvesting causes physiological stress, mostly due to water loss and wilting, and damaged surfaces may release nutrients for microbial development. This stress may also allow the endophytic flora to flourish, which would otherwise be dormant.
  9. The softening of tissue caused by bacteria’ pectinolytic activity is the most common type of deterioration. Pectin, a key component of the intermediate lamella between the cells, is involved in the microorganisms’ breakdown process.

BACTERIAL AGENTS

  1. Pectinolytic species of the Gram-negative genera-
  2. Pectinobacterium
  3. Pseudomonas
  4. Xanthomonas

These microbes are considered important in the spoilage of potatoes, under some circumstances.

  • Non- sporing Gram-positive organism Corynebacterium sepedonicum causes a ring rot of potatoes.

The bacteria most commonly associated with the soft rotting of carrots are Pectobaterium spp. Such as:

  • P.carotovorum subsp. carotovorum
  • P.carotovorum subsp. odoriferum

FUNGAL AGENTS

Spoilage conditions in vegetables are usually initiated pre-harvest and sometimes post-harvest.

Botrytis cinerea causes grey mould rot in a variety of vegetables such as:

  • Asparagus
  • Lettuce
  • Onions
  • Cabbage
  • Garlic
  • Celery

In this disease, the casual fungus grows on decayed areas in the form of prominent grey mould. Rhizopus soft rot, caused by the fungi Rhizopus stolonifer is responsible for turning vegetables soft and mushy. Among those affected are beans, carrots, sweet potatoes and tomatoes.

Blue mould rot is a post-harvest disease of apples and pears, caused by Penicillum enpansum.

CONSEQUENCES OF SPOILAGE

Vegetables are not usually a cause of public health concern but transmission of enteric pathogens such as:

  • Salmonella
  • Shigella
  • VTEC

Direct contamination from farmworkers and animal excrement, the use of manure or sewage sludge as fertiliser, or the use of polluted irrigation water are all possibilities.

  1. Celery, watercress, lettuce, cabbage and beansprouts have all been associated with Salmonella infections, including typhoid and paratyphoid fevers. Moreover, an outbreak of Shigellosis gas has been traced to commercial shredded lettuce.
  2. Not all pathogens are necessarily transmitted to vegetables by direct or indirect fecal contamination. Organisms such as Clostridium botulinum have a natural reservoir in the soil and any products contaminated with soil can be assumed to be contaminated with soil can be assumed to be contaminated with spores possibly in very low numbers.
  3. Psychrotrophic species Listeria monocytogenes caused an outbreak of listeriosis in USA (1979) and can easily grow on shredded cabbage and salad vegetables at temperatures as low as 50C and modified- atmospheres have no effect on this organism.