Safety and spoilage of fermented foods1

Safety and Spoilage of Fermented Foods

FOOD SAFETY

The assurance that food will not cause harm to the consumer when it is prepared and/or eaten according to its intended use.

• Should not be confused with FOOD HYGIENE, which is defined as all conditions and measures necessary to ensure the safety and suitability of food at all stages of the food chain.

• The No. 1 concern in the food industry

• Has been a source of concern to humankind since the dawn of history

Properties of Fermented Foods

• Enhanced preservation

• Enhanced nutritional value

• Enhanced functionality

• Enhanced organoleptic properties

• Unique

• Increased economic value

Safety of Fermented Foods

Fermented foods are safer than their unfermented counterpart owing to the following:

• Inhibition of the growth of most pathogenic bacteria

• Removal of natural toxic components

• Inhibition of the formation of bacterial toxins

Safety of Fermented Foods

The improved food safety arising from fermentation is largely due to lactic acid bacteria, a group of organisms that predominate in most fermented foods. Their growth and metabolism inhibit the growth of normal spoilage flora of the food material and of any bacterial pathogens that it may contain.

HOWEVER, a number of food-borne hazards are not controlled by lactic acid fermentation and so present a serious threat to health if they persist in food. Examples are the following:

• Enterohemorrhagic E. coli has shown pattern of acid resistance and may survive certain fermentation processes. Yoghurt and fermented meat have been recognized as potential vehicles of infection by this microorganism.

• Food and water-borne viruses, a frequent cause of gastroenteritis, may survive high levels of acidity.

• Most toxins produced by some algae, bacteria and molds are also unaffected by fermentation.

THUS, it is crucial NOT TO RELY ONLY on fermentation to eliminate or reduce hazards to safe levels.

For this reason, fermentation are frequently combined with other processes such as soaking, washing, cooking and pasteurization to ensure adequate safety.

In addition, it is important to observe good food safety practices to ensure fermented food safety. These include the following:

• Ensuring that the starting materials used did/do not come into contact with manure or compost

• Using good fresh food as starting materials

• Using only starting products from healthy animals.

• Observing appropriate levels of hygiene and sanitation to avoid contamination during handling.

• Observing proper fermentation procedures.

In essence, this means examining the fermentation process carefully and developing a plan where hazards associated with the different production steps are considered and controlled. In this regard, the Hazard Analysis and Critical Control Point (HACCP) is the standard method of food safety assurance.

A system that identifies, evaluates and controls hazards which are significant for food safety.

• It is a scientific, rational and systematic approach to identifying, assessing, and controlling hazards during production, processing, manufacturing, preparation and use of food to ensure that food is safe when consumed.

• Conceived in the 1960s by the Pillsbury Company, NASA and the U.S. Army Laboratories at Natick to ensure the safety of foods for astronauts.

• In the 50 years since its conception, it has grown to become the universally recognized and accepted method of food safety assurance.

HACCP

Principles of HACCP

1. Conduct a hazard analysis

2. Identify critical control points

3. Establish critical limits for each critical control point

4. Establish critical control point monitoring

requirements

5. Establish corrective actions

6. Establish procedures for ensuring the HACCP

system is working as intended

7. Establish record keeping procedures

Despite the low pH or ethanol content of

fermented food and beverage products, which

prohibit the growth of pathogens, spoilage CAN still OCCUR.

Spoilage of Fermented Foods and Beverages

MAJOR CAUSES OF FOOD DETERIORATION

• Growth and activities of microorganisms (bacteria, yeasts and

molds]

• Activities of food enzymes and other chemical reactions within the food itself

• Infestation by insects (parasites and rodents)

• Inappropriate temperature for a given food

• Either the gain or loss of moisture

• Reaction with oxygen

• Exposure to light

• Physical stress or abuse

• Time

Beer and wine (pH 4-5) can be spoiled by yeasts and

bacteria. The bacteria involved are primarily lactic acid bacteria like

lactobacilli and Pediococcus spp., and (under aerobic conditions) acetic

acid bacteria like Acetobacter and Gluconobacter species. Acetic acid

bacteria convert ethanol to acetic acid in the presence of oxygen.

However, the anaerobic bacterium Megasphaera cerevisiae can also

spoil beer by producing isovaleric acid and H2S.

bacteria

Packaged beer undergo spoilage owing to the growth of the

yeast Saccharomyces diastaticus, which grows on dextrins that

brewer’s yeast cannot utilize.

Candida valida is the most important spoilage yeast in wine. In

either case, spoilage by yeasts results in the development of

turbidity, off flavors and odors.

Wines can also be spoiled by lactic acid bacteria, which

convert malic acid to lactic acid (malo-lactic fermentation). This

reduces the acidity of the wine and adversely affect wine

flavor. In some areas, wine grapes have too much malic acid so

its fermentation is deliberately used to reduce the acidity of

grape juice that will be used for wine.

Fermented vegetables such as sauerkraut and pickles, as well

as other acid foods like salad dressings and mayonnaise, can

be spoilt by yeasts, molds and lactic acid bacteria. Spoilage in

fermented vegetables is often manifested by off odors or

changes in the color (chromogenic colony growth) or texture

(softening) of the product. In mayonnaise or salad dressing, the

first signs of spoilage are usually off odors and emulsion

separation.

Cottage cheese can be spoiled by yeasts, molds and bacteria.

The most common bacterial spoilage is “slimy curd” caused

by Alcaligenes spp. (gram-negative aerobic rod bound in soil,

water, and intestinal tract of vertebrates). Like Campylobacter,

these species do not oxidize carbohydrates, but instead use

amino acids and TCA intermediates.

Penicillum, Mucor and other fungi also grow well on cottage

cheese and impart stale or yeasty flavors.

Ripened Cheeses, despite their low aw, low pH, and high

salt concentration, which inhibit most spoilage

microorganisms, are spoiled by surface mold growth.

Spores of C. butyricum, C. sporogenes and others can

germinate in cheeses (e.g., Swiss) with intrinsic properties

that are less inhibitory (e.g., lower salt concentration, higher

pH).

These organisms may metabolize citrate, lactose, pyruvate

or lactic acid and produce butyrate or acetate plus CO2 or

H2 gas which “blows” the cheese.

Advances in Food and Beverage Fermentation

1. Engineering of microorganisms for improved fermentation

• Development through genetic techniques of robust proprietary microorganisms that can better ferment substrates to produce the desired products.

• Engineering of innovative microbial strains that can help produce biomolecules in bulk using improved technologies These developments are indicative of the huge potential of fermentation as a low-cost and flexible method of producing a range of end products.

• Recombinant DNA technology can be used to genetically improve bacterial strains for use in industrial processes. Specific genes can be partially or totally eliminated from a strain or replaced with different alleles from other strains of the same genus. Likewise, new properties can be introduced into a strain by gene transfer.

2. Metabolic pathway engineering of various enzymes

Lactic acid production is dependent on lactate dehydrogenase (LDH) activities present in lactic acid bacateria. The lactic acid stereoisomerism is, in general, controlled by the enzymatic activity of LDH-L or LDH-D, although, in some cases, lactate racemaseshave been detected. Hence, lactic acid bacteria that contain only one of these LDH enzymes may produce a pure enantiomer. Lactobacillus helveticus has been the first lactic acid bacterium to be used and combined with LDH-D inactivation, a derivative developed that was able to produce pure L-lactic acid. By using a similar approach, pure enantiomers of lactic acid have also been obtained by the inactivation of specific LDH in other lactic acid bacteria.

Advances in Food and Beverage Fermentation

3. Improvement of the rheological properties of fermentation broths.

4. Development of more efficient process-driven technologies

Examples: solid-state fermentation, consolidated bioprocessing, ultrasonication, syngas fermentation, and dark fermentation

5. New bioreactor designs

Examples: High-mass transfer chemical reactors for methanotrophfermentation and versatile tray-type solid-state fermentation bioreactors

Advances in Food and Beverage Fermentation