No abstract

Ten fishmeal samples (hidden duplicates of 4 meals plus 2 high-protein meals as a Youden pair), tryptophan, and nicotinic acid were analyzed by 18 laboratories using the Dumas method. Thirteen of the laboratories also analyzed the same 12 samples using their current Kjeldahl method. Recoveries (± sR) of tryptophan and nicotinic acid were 99.3 ± 1.04 and 98.8 ± 2.11 by Dumas and 97.1 ± 3.03 and 74.6 ± 26.76 by Kjeldahl. The Dumas method gave significantly greater values (P < 0.001) than the Kjeldahl method. For fishmeals, Kjeldahl N 0.989 of Dumas N (P < 0.001). A similar proportionate difference (0.984 of Dumas N) was observed with tryptophan. Most laboratories failed to determine nicotinic acid correctly by Kjeldahl. For fishmeals, the relative standard deviations for repeatability and reproducibility were for Dumas 1.48 and 2.01% and Kjeldahl 1.62 and 2.37%, respectively. A single analysis conducted in 2 laboratories should not differ by more than 5.63% of the mean value when measured by Dumas or by more than 6.64% by Kjeldahl. It is concluded that with fishmeal, Dumas gives a more reliable measure of organic nitrogen than Kjeldahl, and, therefore, Dumas should be the method of choice.

ABSTRACT. The purpose of this work was to evaluate the use of antioxidants in extending the shelf‐life of mayonnaise constantly exposed to air in which all of the oil ingredient was fish oil. Mayonnaise prepared without antioxidants had a shelf‐life at room temperature of approximately 1 day. Citric acid or sodium citrate and propyl gallate in the oil phase and EDTA and ascorbic acid in the aqueous phase increased the shelf‐life to an average of 49 days at room temperature as judged by sensory evaluation. With refrigeration, the number of days to off‐odor development was increased to 89. With the addition of an oxygen scavenging system of glucose oxidase‐catalase‐glucose, the shelf‐life increased to an average of 132 days. Both oxygen and light were shown to be detrimental to the stability of the product. Considerable variation was observed between batches of menhaden oil, the primary fish oil used in formulating the mayonnaise in these studies.

Twenty‐two laboratories participated in a collaborative test to determine the iodine value (IV) of eight samples of fish oil (four with IV<150, four with IV>150) with either carbon tetrachloride (AOCS Official Method Cd 1–25) or cyclohexane (AOCS Recommended Practice Cd 1b‐87) as solvent and either 1 or 2 h of reaction time. Laboratories received coded duplicate samples (hidden duplicates) and carried out duplicate determinations on each oil by each solvent‐time combination (open duplicates). Replacing carbon tetrachloride with cyclohexane resulted in a lower IV (P<0.001). The decrease averaged 1.6 IV units for low‐IV oils and 3.8 IV units for high‐IV oils; this difference in response of 2.2 IV units between low‐ and high‐IV oils was significant (P<0.001). Increasing the reaction time had a relatively small effect (0.34±0.18). There was no interaction of reaction time with solvent or oil type. Cyclohexane caused emulsions, which made it difficult to titrate residual iodine and thus increased the variability of the determination. The repeatability standard deviations (sr), based on hidden duplicates, for 1‐h reaction time with carbon tetrachloride and cyclohexane were 2.17 and 3.35, respectively. The corresponding reproducibility standard deviations were 2.73 and 4.53.