Search

The occurrence and heat inactivation of native and bacterial lipases and proteinases in milk were studied.Production of these enzymes by Gram-negative psychrotrophic bacteria in milk was found to take place towards the end of exponential growth and in the stationary growth phase.Kinetics of heat inactivation in milk of milk lipoprotein lipase, alkaline milk proteinase and lipases and proteinases of some Gram-negative bacteria are given.The effects of residual lipolytic and proteolytic activity on the keeping quality of milk products were studied. In order to prevent activity of native lipases and proteinases, the milk should be heated sufficiently. The only way of preventing activity of bacterial lipases and proteinases in milk is to take measures against the growth of Gram-negative bacteria in the milk to be processed.

Ontwlkkeling van een snelle en nauwkeurige methode voor het bepalen van vitamine-A in margarine, halvarine e.d. m.b.v. vloeistofchromatografie (HPLC) . Vitamine A wordt in dit onderzoek bepaald na verzepen, aanzuren en oplossen in acetonitril. De vrije vetzuren slaan neer in acetonitril terwijl vitamine A in oplossing blijft. Door een "clean-up" toe te passen, is een voldoende zuivere oplossing van vitamine A te verkrijgen, welke geschikt is voor analyse met HPLC. Het is mogelijk om op deze wijze vitamine A kwantitatief en goed reproduceerbaar te bepalen.

Literatuuroverzicht analysemethodes voor vitamine C in voedingsmiddelen. Voor de bepaling van AA in verse groenten en fruit verdient het aanbeveling de HPLC methode (2.6.3) op te starten. Gezien de potentiële mogelijkheden van HPLC is het nuttig de toepasbaarheid voor een breder skala produkten te onderzoeken. Daarnaast is het noodzakelijk te beschikken over een methode waarvan aangenomen mag worden dat hiermee voor een groot aantal produkten betrouwbare resultaten verkregen kunnen worden. Methode 2.4 is hiervoor het meest geschikt.

Een overzicht wordt gegeven van de gevonden gehaltes aan: vocht, vet, vitamine A, docoseenzuur, de verhouding van plantaardige en dierlijke oliën en vetten en het nettogewicht, ingedeeld per fabriek.

A method was devised for estimating vitamin D in roughages. After boiling with 10 % alcoholic KOH the material was extracted with petroleum ether, and purified by chromatography through an activated alumina column with petroleum ether. Chromatography removed an unsaponifiable factor antagonistic to vitamin D. The eluate was assayed by the curative X-ray method against a vitamin D standard with white rats.No vitamin D could be detected in ensiled turnips. Average contents in roughages under Dutch conditions were: grass silage and artificially dried grass about 300 IU, hay cured in windrows and cocks 1000 IU, frame-dried hay 575 IU and straw possibly as windrow hay. Considering the usual rations and the great variation in vitamin D in hays the intake of the vitamin might not be adequate on all farms. Although identification of the antagonistic factor was not possible a relation appeared. to exist between the factor and carotene. Synthetic carotene and vitamin A palmitate 100-800 IU daily showed in rats a weak antagonism of a competitive nature. Vitamin A excess in lambs had no effect on serum calcium but lowered serum inorganic phosphorus.

A method was devised for estimating vitamin D in roughages. After boiling with 10 % alcoholic KOH the material was extracted with petroleum ether, and purified by chromatography through an activated alumina column with petroleum ether. Chromatography removed an unsaponifiable factor antagonistic to vitamin D. The eluate was assayed by the curative X-ray method against a vitamin D standard with white rats.No vitamin D could be detected in ensiled turnips. Average contents in roughages under Dutch conditions were: grass silage and artificially dried grass about 300 IU, hay cured in windrows and cocks 1000 IU, frame-dried hay 575 IU and straw possibly as windrow hay. Considering the usual rations and the great variation in vitamin D in hays the intake of the vitamin might not be adequate on all farms. Although identification of the antagonistic factor was not possible a relation appeared. to exist between the factor and carotene. Synthetic carotene and vitamin A palmitate 100-800 IU daily showed in rats a weak antagonism of a competitive nature. Vitamin A excess in lambs had no effect on serum calcium but lowered serum inorganic phosphorus.

An attempt was made to explain the great variation in vitamin C content in garden crops, so that vitamin C content may be increased by altering the influencing factors. Ascorbic acid content (AA-ct) was estimated by titration with 2,6-dichlorophenolindophenol. Differences in AA-ct between plant varieties were attributed to polyfactorial genetic differences. Between the AA-ct's of (sub-units of) different genera no correlation with taxonomic order could be found.AA-ct of rose hips was correlated to the ratio K: Ca: Mg in ash. At the green stage AA-ct was highest when none of the cationic ratios deviated from the average. The same held for the coloured hips, but with other averages (higher K%) and higher AA-ct's. The ideal curve of AA-ct during fruit development may be modified by the weather. A maximum usually occurred in ripe fruit. In leaves it varied with incident solar energy; dehydroascorbic acid showed the opposite course.Growth substances strongly influenced both ascorbic acid and total vitamin C in the bark of cuttings and in germinating peas. After its formation from sugars, AA acts, particularly on chloroplast surfaces, as a transporter of H from chlorophyll. There it acts as a hydrogen donor and buffer.

An attempt was made to explain the great variation in vitamin C content in garden crops, so that vitamin C content may be increased by altering the influencing factors. Ascorbic acid content (AA-ct) was estimated by titration with 2,6-dichlorophenolindophenol. Differences in AA-ct between plant varieties were attributed to polyfactorial genetic differences. Between the AA-ct's of (sub-units of) different genera no correlation with taxonomic order could be found.AA-ct of rose hips was correlated to the ratio K: Ca: Mg in ash. At the green stage AA-ct was highest when none of the cationic ratios deviated from the average. The same held for the coloured hips, but with other averages (higher K%) and higher AA-ct's. The ideal curve of AA-ct during fruit development may be modified by the weather. A maximum usually occurred in ripe fruit. In leaves it varied with incident solar energy; dehydroascorbic acid showed the opposite course.Growth substances strongly influenced both ascorbic acid and total vitamin C in the bark of cuttings and in germinating peas. After its formation from sugars, AA acts, particularly on chloroplast surfaces, as a transporter of H from chlorophyll. There it acts as a hydrogen donor and buffer.