Three trials were carried out to determine the suitability of locally produced palm kernel meal ( P K M ) as the major protein concentrate in the diets of weaners, growers and fattening pigs in the tropics. Large White and Large White x Landrace cross barrows and gilts were used. These were individually fed at semirestricted levels the various diets formulated to contain approximately 15, 12 and 16.5 % crude protein for trials 1, 2 and 3 respectively, the PKM or other protein sources contributing at least 50% of the total dietary protein in all the diets. In trial 1, pigs on the PKM diet grew at a lower rate, had poorer feed:gain ratio and protein efficiency ratio and lower feed consumption than the pigs on other diets. Pigs on a fish meal diet (FM) had the best performance throughout. In trial 2, the same trends as for trial 1 were observed, except that pigs on the dried skimmed milk (DSM) diet performed better than those on all other diets. In trial 3, the pigs on the PKM diet supplemented with 10% groundnut cake or 15% DSM had slower growth rate and lower feed:gain ratio than the pigs on other diets containing lower quantities of PKM supplemented with fish meal (FM) or blood meal (BM).

Seven chemical methods, namely peroxide value (PV), totox value (TV), anisidine value (AV), conjugable oxidation products (COP), oxodiene value (OV), induction period (IP), iodine value (IV) and a sensory analytical procedure (flavour score, FS) have been used in evaluating the oxidation state of groundnut oil heated at 100°C for varying lengths of time up to 20 h. As oxidation progressed, PV, TV, AV, COP and OV increased. IP and IV decreased with oxidation while FS showed a progressive deterioration on a seven-point scale from bland to very rancid. On the basis of sensitivity to oxidative changes, five of the methods (PV, TV, IP, IV and FS) were found to be satisfactory. However, the best correlation with flavour scores were obtained in the case of IP, IV and OV while AV and COP correlated poorly with FS. Three methods (PV, IP and IV) best satisfied the combined criteria of sensitivity to oxidative changes and correlation with flavour.

Single-cell proteins have significant potential for use as food additives or as major components of processed foods. However, a number of problems associated with single-cell protein have to be solved to render it a safe and cheap source of protein for human use. Proteins from yeast cells should be low in cell wall fragments to maximise nutritional value; nucleic acid (essentially RNA) content should be minimised to reduce its intake to less than 2 g per day: the protein should have acceptable colour, flavour and texture. The above requirements can be met if suitable methods for the extraction and isolation of the protein from cellular material can be achieved economically.Our initial studies with single-cell proteins have centred on baker's yeast containing more than 10 % nucleic acid.The first requirement of the investigation, 100 % disintegration of the yeast cell walls, has been achieved by mechanical agitation in aqueous suspension. Ultrasonication and enzymic degradation both succeeded only partially. The disintegrator was of 500 ml capacity, handling yeast suspension in a mild steel vessel with a high-powered stirrer agitation in the presence of Ballotini beads. Disintegration was monitored by counting intact cells under the microscope after staining with methylene blue. A supplementary staining technique for cell walls provided confirmatory indication of the site of breakage. Protein was extracted from the disintegrated biomass by adjusting the pH to 11.8 and centrifuging the resulting slurry. The supernatant was either (a) incubated with salt to activate endogenous enzymes capable of degrading nucleic acids, or (b) brought to pH 4.5 to precipitate protein isolate at its iso-electric point. In the former case, after incubation, a second isolate, low in nucleic acids was obtained by method (b). Both isolates as well as cell-wall material were stored after freezedrying.Various parameters have been modified in these studies in order to optimise protein yield and quality. The protein content rose from 55 % in the freeze-dried intact yeast cells to above 90% in the isolates. The amino acid profiles of the protein preparations were satisfactory: nucleic acid levels were reduced to about one-quarter of their original value.