Stability of vitamins during the storage of liquid infant milks.

The stability of the water-soluble B vitamins and the fat-soluble vitamins A and E of three liquid infant milks was followed throughout 12 months of storage at 20, 30 and 37 degrees C. Two samples were 'follow-on' milks from two different manufacturers and the other a 'junior' milk from one of these. The levels of water-soluble vitamins and vitamin E remained constant during storage at the three temperatures. In contrast, vitamin A decreased in samples from one manufacturer at all storage temperatures, and in samples from the other only at 37 degrees C. A kinetic equation was derived that made it possible to predict the influence of storage temperature on the shelf life of these kinds of products, together with the storage period during which levels of vitamin A recommended as adequate would remain.

Progress of browning reactions during storage of liquid infant milks.

Changes in furfural compounds and reactive lysine were monitorized in three commercial liquid infant milks during 9 months of storage at 20, 30, and 37 degrees C. Samples consisted of two ultrahigh temperature (UHT)-treated milks and one conventionally sterilized milk. Reactive lysine remained constant throughout storage at the three temperatures, whereas, in general an increase in furfural compounds was observed. The heat treatment used in the manufacture of milk is an important factor that influences the levels of furfural compounds although the composition of the milk is also a critical factor. Finally, a study was conducted to find the kinetic equations describing furfural compounds changes and allowing for the prediction of the influence of time and temperature of storage on those changes.

Determination of available lysine in infant milk formulae by high-performance liquid chromatography.

A high-performance liquid chromatography (HPLC) method to determine available lysine is proposed. Available lysine was measured by an optimised fluorodinitrobenzene method on the basis of the reactivity of the free epsilon-amino group of the lysine. The classical acid hydrolysis has been improved and shortened from the usual time of 12 h to 2 h 30 min using an oil bath. Optimal resolution and quantitation of Nn-dinitrophenyllysine was obtained with a Nova-Pak C18 column using an isocratic elution with 35% methanol and 65% 0.01 M sodium acetate buffer (pH 4.5) and a flow-rate of 1 ml/min. Satisfactory results were obtained for the reliability of the method in terms of linearity from 0.1 to 5.0 mg/l of lysine-free base, precision (R.S.D. values between 4.3% and 7.8%), recovery (91.5%) and sensitivity (detection limit of 0.02 mg/l). The proposed method has also been checked for lack of interferences from other dinitrophenyl-amino acids.

Determination of vitamins A and E in infant milk formulae by high-performance liquid chromatography.

A high-performance liquid chromatographic (HPLC) method was developed for the determination, in one run, of retinol and alpha-tocopherol in infant milk formulae. The method involved saponification at room temperature and a later extraction of vitamins with n-hexane. The vitamins were resolved with a C18 reversed-phase column and they were detected by UV spectrophotometry. Linearity, precision, recovery and sensitivity were satisfactory. The main advantage of the method proposed is the simultaneous determination of both vitamins using a common extraction procedure and UV detection with a variable-wavelength spectrophotometer.

Determination of water-soluble vitamins in infant milk by high-performance liquid chromatography.

A rapid, simple and reliable liquid chromatographic method has been developed for the simultaneous determination of nicotinamide, thiamin, riboflavin, pyridoxine, pyridoxal, pyridoxamine, cyanocobalamine and folic acid in liquid and powdered infant milk. Ion-pair chromatography with a reversed-phase C18 column is used. Six vitamins were resolved in a single analysis; total analysis time never exceeded 55 min. A mobile phase of methanol-water (15:85), 5 mM octanesulfonic acid, with 0.5% triethylamine at pH 3.6 and a flow-rate of 1.0 ml/min gave the most satisfactory separation of these vitamins using a UV detector set at different wavelengths. Sample preparation involves acidification to precipitate proteins, and centrifugation followed by gravity filtration. Linearity, precision, recovery and sensitivity were always satisfactory. Detection limits ranged from 0.02 to 0.10 microgram/ml and determination limits ranged from 0.03 to 0.25 microgram/ml.

Biogenic amines in Spanish beers: differences among breweries.

Ten biogenic amines in Spanish beers were studied using HPLC, Agmatine, tyramine and putrescine were the prevailing amines, while histamine, beta-phenylethylamine, tryptamine, cadaverine, spermine and spermidine were detected at relatively low levels (in general < 2 mg/l). On the basis of the wide range of levels observed for tyramine (from 1.90 to 31.55 mg/l), the consumption of beer requires restriction in patients receiving monoamine oxidase inhibitor drugs. Biogenic amine levels in beers of the same type from the same company and from different companies were monitored every month over 1 year. Agmatine and putrescine levels showed minimal fluctuations in beers from the same company as well as from different breweries. Raw materials and brewing conditions would not affect the levels of those amines. However, tyramine levels were subject to wide fluctuations in beers produced by particular breweries irrespective of whether they were produced by the same company. Relatively high levels of tyramine were specific to some breweries.

Changes in Biogenic Amines during the Manufacture and Storage of Semipreserved Anchovies †.

Biogenic amines were determined by using high-pressure liquid chromatography during spoilage of raw Engraulis encrasicholus (anchovies), during ripening and shelf life. Histamine, cadaverine, tyramine, and putrescine were extensively formed at the beginning of spoilage, while ß-phenylethylamine and tryptamine were formed only at advanced stages of spoiling. Serotonin, spermine, and spermidine levels were constant throughout spoilage. Seventeen lots of anchovies were evaluated through the typical ripening process. Each ripening process lasted 18 to 22 weeks, Only a slight formation of biogenic amines was observed during the first period of ripening (2 to 4 weeks). According to our results, ripening had little influence on the formation of amines, and therefore the amount of amines in the final products depends primarily on the levels of these substances in the raw material. During shelf-life studies, anchovies packed in brine were more stable, from the point of view of biogenic amine formation, than anchovies packed in oil. High formation of tryptamine and histamine was observed in both products when they were stored at room temperature. Refrigerated storage prevents amine formation.