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Nonprotein nitrogen content of defatted jojoba meals
Author(s) -
Wolf Walter J,
Schaer Mardell L,
Abbott Thomas P
Publication year - 1994
Publication title -
journal of the science of food and agriculture
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.782
H-Index - 142
eISSN - 1097-0010
pISSN - 0022-5142
DOI - 10.1002/jsfa.2740650304
Subject(s) - nitrogen , chemistry , solubility , fraction (chemistry) , extraction (chemistry) , chromatography , isoelectric point , trichloroacetic acid , non protein nitrogen , food science , biochemistry , organic chemistry , enzyme
Extraction of defatted jojoba meals with 0–5 M triehloroacetic acid solutions revealed a minimum solubility of nitrogenous compounds in the range of 0.5–2 M . This minimum was assumed to correspond to the nonprotein nitrogen (NPN) fraction. Trichloroacetic acid concentrations of 0.8–1.0 M were found to be optimal for NPN determination. NPN values for laboratory‐prepared meals ranged from 21 to 29% of the total nitrogen for undecorticated (with seed coat) meals and from 21 to 30% for decorticated (without seed coat) meals. Commercial presscakes and presscake fines ranged from 15 to 20% of total nitrogen as NPN. These lower values apparently reflect heat treatments received by the presscakes during commercial expelling of the jojoba liquid wax esters, In aqueous dispersions of unheated jojoba meals, nitrogenous compounds exhibited a minimum solubility of 23–45% of total nitrogen at pH 3–4, the apparent isoelectric region of the storage proteins. In some meals NPN comprised up to 100% of the nitrogen soluble at this minimum; thus, low yields of recoverable meal nitrogen in the form of protein isolates are predicted. The NPN fraction was characterized by amino acid analysis and gel electrophoresis and found to contain free amino adds, peptides, and polypeptides of 6–10 kDa. Simmondsin and its derivatives are estimated to make up about one‐third of the NPN.