BUTTERFAT OXIDATION

Evening Post, Volume CXIX, Issue 24, 29 January 1935, Page 16

BUTTERFAT OXIDATION

FLAVOURS AND ODOURS

QUESTION OF ELIMINATION

"The oxidation of buttcrfat and oxidation flavours" was the title of a paper read at the recent conference at Hamilton of tho Institute of Chemists of Great Britain, New Zealand section, and the New Zealand lnstituto of Chemists, Mr. Williams, of tho New Zealand Co-operativo Dairy Company, being the speaker. Ho remarked that tho most important constituent of butterfat studied in the past had been butyric acid. The production of free fatty acids in dairy products was due mainly to the action of enzymos. The lower acid, butyric, due mainly to tho action of enzymes, was responsible for rancidity flavours and odours. It was also apparent that somo of the degradation products of rancidity due to tho formation of increased quantities of oxidisable constituents might cause oxidation changes simultaneously. The high temperature of pasteurisation of dairy products which rendered the lipases or fat-splitting enzymes inert had almost completely overcome this defect in our product. Checks on the total bacterial, yeast, and mould 'content of butter were not only a check on the efficiency of pasteurisation but also on factory plant contamination. Tho production of , fishy flavours in dairy produce and its association with rancidity and oxidation flavours bad involved a study of the phospholipid lecithin. Investigations indicated that the presence of highly-acid conditions produced the hydrolysis of lecithin with the formation of trimethylamine, which was responsible for the fishy flavour. Very careful attention had therefore been given to the neutralisation of cream for butter-making and the determination, of tho pH of a large number of butter samples. This fishy flavour was also encountered especially on the surface of our packed butters after storage or exposure to light. Light or metallic contaminated wrappings accelerated the hydrolysis of lecithin, lo reduce tho contamination due to1 copper, specification had been mado reducing tho copper content of parchment wrappings from 40 to 10 parts per million. Contamination of butter' *t various stages had shown sources of contamination by metals hitherto thought perfectly safe, and these had been removed. As oleic acid was the only unsaturatcd acid in butter, this had been used for the investigation of oxidation changes. Butterfat when oxidised produced intense tallowy flavours. /# The peroxide test for determining incipient oxidation was of little value in determining whether flavours were due to oxidationl American workers had shown that flavour defects did not always follow the peroxido content and that storage in light played a very important part. Schibstcdfc method of determining aldehydes had been used, and the results at once indicated that by this method incipient oxidation changes might, be detected and checked. Amongst the many«factors which had been investigated as accelerators in producing oxidation of butteTfat were heat, light, acidity, enzymes, and metals. Metals and their salts, awing to their catalytic action, had been'extensively investigated. Copper, owing to the ease with which it passed from one oxide to another, was known as an excellent catalyst for the oxidation of organic compounds. The effect of exposing butterfat to light, especially sunlight, was perhaps the most important factor in causing oxidation flavour jn butterfat. Cream that had been exposed to sunlight for only 15 to 30 minutes, when mado into butter was readily selected by expert butter graders as containing oxidation flavours. This defect in cream was the most difficult with which chemists had to contend, as they had no methods of judging whether the cream had been exposed to sunlight before it reached the factory. ' ' During the discussion it was pointed out that tho assumption had been made that it was only the unsaturated oleic acid which was attacked during oxidation. Experiments at Auckland University had shown that even some of the most stable saturated compounds wore capable of oxidation, under similar conditions. It was suggested that this might open up a new field of mvestigatiou. References were mado to the action of direct sunlight- on milk stored in glass bottles. Several cases were mentioned of milk having become sour in a very short time when stored under those conditions. The necessity of storing milk in tho dark or in dark-coloured bottles was emphasised.