The lactoperoxidase system (LP-system) is an acceptable chemical method for raw milk preservation, especially in rural areas where refrigeration facilities are absent to farmers. Milk production in most African countries is dominated by small-scale traditional production systems using low yielding local breeds. Therefore, processors who operate in such situations must rely on small volumes of milk from many farmers. Application of the LP-system prolongs the shelf life of raw milk and also encourages grouping of farmers hence facilitating milk collection by processors. The application of the LP-system is a recent preservation method for milk in Cameroon whose efficiency has been proven. Therefore, need arose for further studies on the influence of this method on milk processing as well as the quality dairy products. The LP-system was activated by adding 10 ppm sodium thiocyanate and 8.5 ppm sodium percarbonate to fresh milk. Yoghurt and Bambui cheese were processed separately from treated and untreated (control) milk samples. Yogurt was produced from both the treated and the control milk samples at 2%, 3%, 4% and 5% (v/v) culture levels. Yogurt samples were analysed for acidity, protein content and dry matter content while cheese was analysed for butterfat and moisture content. Statistical tests were conducted by Analysis of Variance using the Fisher's test. Simple organoleptic assessments were conducted to compare yogurt and cheese from the treated and the control milk. Activation of the LP-system delayed lactic acid formation in yogurt during incubation and storage leading to increased energy consumption during processing and an improved keeping quality during storage. LPsystem treatment reduced the overall organoleptic quality of yogurt while it improved on that of Bambui cheese. Dry matter content and fat content of yogurt were not significantly affected by LP-system treatment (P<0.05). LP-system treatment did not also affect the moisture and fat content of cheese but slightly improved on its yield.

Des données sur 275 lactations collectées entre 1981 et 1991 ont été analysées. Le but de ce projet a été d’étudier l’effet de la saison de vêlage, de quelques paramètres zootechniques, de l’intervalle entre vêlages des races Holstein et Jersiaise et de leurs croisements avec le zébu Goudali et le zébu Peul blanc (White Fulani) sur la production laitière dans les hauts plateaux de l’ouest du Cameroun. Les résultats suivants ont été obtenus : - la production laitière des races pures Holstein (n = 73) et Jersiaise (n = 32), sans être comparable à celle de leur pays d’origine, a été significativement supérieure à celle des autres types génétiques étudiés, la Holstein ayant été plus performante que la Jersiaise (2 508 ± 105 l en 291 ± 10 jours, contre 1 818 ± 137 l en 251 ± 13 jours) ; - en croisement de première génération avec le zébu local, la Holstein (n = 52) a produit significativement plus de lait que la Jersiaise (n = 57). La Holstein x le zébu Goudali a produit plus de lait que la Jersiaise x le zébu Peul blanc (1 940 ± 109 l en 270 ± 10 jours, contre 1 550 ± 106 l en 257 ± 10 jours). La production laitière des races croisées trois quarts Jersiaises (n = 61) a été plus élevée (1 774 ± 117 en 250 ± 11 jours) ; - l’année et le numéro de lactation ont influencé significativement la production laitière et la durée de lactation, alors que la saison de vêlage n’a pas eu d’effet significatif sur ces deux paramètres. L’analyse financière et les recherches sur la composition du lait devraient se poursuivre pour des recommandations plus concrètes.

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In order to determine a suitable temperature and time combination for the proper pasteurization of milk under conditions in Cameroon, the destructive effects of heat on the peroxidase and micro‐organisms in local milk were studied. In the first step, fresh milk samples were heated at temperatures of 64–100°C for 1 min. Peroxidase was found to be sensitive to heat treatment at temperatures of 74–76°C and completely destroyed above 78°C. In the second step, fresh milk samples were heated to 74°C and held at that temperature for 15 s, 5 min, 10 min, 15 min or 20 min; microbiological analyses revealed that survival rates were 56.7, 1.5, 0.2, 0.06 and 0.05%, respectively. Peroxidase was completely destroyed after 10 min at this temperature. In terms of microbial quality, there were no significant differences (P < 0.001) between holding times of 10, 15 and 20 min. A heat treatment of 74°C for 10 min yielded milk free of peroxidase and with < 10 000 cfu/mL. It is recommended that raw milk be given at least this treatment to ensure safe milk supplies in Cameroon.