BY-PRODUCTS TECHNOLOGY

Module 3. Processing and utilization of whey

Lesson 27
FERMENTED PRODUCTS FROM WHEY-2

27.1 Introduction

Various fermented products such as organic acids, vitamins, exopolysaccharides and many other products like antibiotics, glycerol etc. can be produced from whey.

27.2 Production of Organic Acids

27.2.1 Lactic acid

Lactic acid is formed by the fermentation of milk sugar (lactose) by Streptococcus lactis and is commercially produced under controlled fermentation of hexose sugar from molasses, corn sulphite waste or whey. Whey has been considered more economical for the commercial production of lactic acid. The starter culture Lactobacillus delbrueckii spp. bulgaricus grows rapidly at 45°C or 50°C and can ferment all the lactose in whey to lactic acid in about 40 h. The use of high temperature is not only favourable to the more rapid growth of the culture, but it is also effective in controlling the development of many contaminants that could grow at lower temperature and reduce the yield of lactic acid.

Whey has been a traditional feedstock for the production of lactic acid and lactate by fermentation. This is typically conducted in batch mode using homofermentative strains of Lactobacillus such as L. bulgaricus, corn-steep liquor and/or other complex nutrients such as malt sprouts, and malt or yeast extracts may be supplemented. The pH is controlled in the range 5.5-6.5 by addition of Ca(OH)₂ or CaCO₃ and the optimum temperature is about 43°C. The medium is usually pasteurized, but the combination of the relatively high temperature with the high acid concentration and large inoculum (5-10% of the fermenter volume) mean that contamination is not a serious problem. For natural-strength whey, the fermentation will be complete in less than 24 hours with a yield of 90-95%.

27.2.2 Ammonium lactate

Whey is used for production of ammonium lactate by the addition of liquid ammonia to the fermentation broth during lactic acid production by L. bulgaricus. After the completion of the fermentation, the broth is evaporated, neutralized by the addition of further ammonia and processed to a range of liquid or solid products. These are used as an animal feed and are especially suitable for ruminants. Ammonium lactate is superior to urea and similar to soya bean meal in its nutritive value and digestibility.

27.2.3 Citric acid

Production of citric acid using whey permeates as one of the substrates has been reported. Maximum yield of citric acid has been obtained usually from sucrose and fructose and in general high concentration of sugar is required to produce high yield of citric acid. However, using a mutant strains of Aspergillus niger during fermentation, citric acid concentration of 8-3g/l representing a yield of 19% (w/s) based on lactose utilized has been observed. Supplementation of permeate with lactose (final concentration of 40 g/l) increased the production to 14.8 g/l (yield 23%); An addition of methanol (concentration 3% v/w) to the fermentation increased the citric acid production to 25 g/l (yield 33% based on lactose utilized).

27.2.4 Propionic acid

Propionic acid is added as a fungistatic agent to bread and bakery products and can be produced by the whey fermentation using strains of Propionibacterium shermanii or P. acidipropionici. Whole whey is typically used and the fermentation must proceed under sterile conditions at around 30°C and pH 6.5-7.5. Nutritional supplements such as yeast extract considerably enhance propionate production and a typical yield of about 40% of the lactose fermented is achieved after 60-70 h. The culture fluid is spray-dried to obtain a power containing both the acid and whey proteins.

27.3 Production of Vitamins

Whey has been used to produce vitamins, mainly riboflavin and vitamin B12. Riboflavin is synthesized by many microorganisms including bacteria, yeasts, and fungi. The first microorganism reported to be capable of producing riboflavin was Clostridium acetobutylicum and subsequently two other microorganisms, ascomycetes, namely, Eremothecium ashbyii and Ashbya gossypii have been reported. The fungus A. gossypii produces a huge amount of this vitamin and is, therefore, used for most of the microbial production processes. Commercial fermentation processes for the production of riboflavin or riboflavin concentrates have been developed. About 30% of the world industrial riboflavin output is produced by direct fermentation with A. gossypii and up to 15 g/l is reported to be the maximum yield.

The pattern of growth and vitamin B₁₂ production by Propionibacterium shermanii has been established in several types of substrates including cheese whey. This organism grows anaerobically and produces propionic acid, which accumulates in the medium. Most industrial processes for the production of vitamin B₁₂ by P. shermanii require neutralization of the accumulated propionic acid to keep the culture growing logarithmically. The formation of vitamin take place during the later part of the fermentation after the organism approaches maximum growth.

27.4 Exopolysaccharides

Whey lactose has been widely used for the production of a large number of exopolysaccharides: dextrans (Leuconostoc mesenteroides), phosphomannans (Hansenula sp.), gellans (Pseudomonas elodea) and several heteropolysaccharides (Streptococcus thermophilus, S. cremoris, S. lactis, Lactobacilus bulgaricus and L. Pastorianus), but lactose needs to be first hydrolysed before being fermented by commercial bacterial strains. Ropy Lactobacillus delbrueckii ssp. bulgaricus has been used for production of exopolysaccharide in sweet whey and simulated whey permeate supplemented with combinations of lactose, KH₂PO₄, NH₄Cl, casamino acids, and mineral salts.

27.5 Miscellaneous

Whey is also used as a raw material for production of various other miscellaneous fermented products. Pediocin has been produced from whey by using different microbial strains. Pediococcus acidilactici NRRL B-5627 is used to produce bacteriocin on whey by batch fermentation. Kluyveromyces marxianus NRRL-665 is commonly used to produce glycerol from whey due to their high growth rate and glycerol yield. Succinate-rich animal feed supplement has also been produced from raw whey with Anaerobiospirillum succiniciproducens by anaerobic fermentation.

Selected references

Gandhi, D.N. 2001. Bioprocessing of whey for lactate production. Indian Dairyman, 53: 8.
Puranik, D.B., Jain, P. and Bandopadhyay, S. 1997. Value added commercial products from whey fermentation. Indian Dairyman, 49 (1): 21-24.
Gassem, M.A., Schmidt, K.A. and Frank, J.F. 1997. Exopolysaccharide production from whey lactose by fermentation with Lactobacillus delbrueckii ssp. bulgaricus. J. Food Sci. 62 (1): 171-173.
Gandhi, D.N. 1989. Production of some useful products of industrial importance through microbial fermentation of whey. Indian Dairyman, 39 (4): 182-184.