A CHEMICAL STUDY OF THE PROGRESSIVE DEVELOPMENT OF OFF‐FLAVOR IN FROZEN RAW VEGETABLES^a

Abstract

It has been known for a long time that unblanched vegetables deteriorate in quality when held in frozen storage for extended periods of time. Rancidity of the lipid matter is one of the primary causes of off-flavor in unblanched peas which had been stored at 0°F. (-17.8"C.) (5). Large increases in acid numbers together with increases in peroxide numbers were observed in the lipids extracted from raw peas after several years of frozen storage. The main increase in acid number occurred during the first year of storage (8). Similar changes were noted in the lipids extracted from unblanched sweet corn, snap beans, and other vegetables after extended periods of storage at 0°F. (-17.8"C.) ( 4 ) .I n order to extend the knowledge of the changes which take place in such material, the present study was undertaken to determine the length of time that unblanched vegetables could be held in frozen storage before these undesirable changes could be detected, and to determine the course of the development of the acids and peroxides during the period of storage. MATERIALS AND METHODSThomas Laxton peas, Wade snap beans, and Golden Cross sweet corn were grown on the Experiment Station farm and were harvested, processed, and stored, as previously described (4, 5 ) .Quality changes were measured both chemically and by means of a taste panel. Samples from each lot were taken for immediate taste test a t the time of harvest, and at regular intervals during storage, until obvious deterioration in quality was definitely established. A t the same time, samples were dried by 1yophiIization and were extracted for 48 hours with peroxide-free anhydrous ethyl ether to obtain the crude lipid material, as described previously ( 5 ) . This work was started before it was determined that a 24-hour extraction period was sufficient to effect the extraction of the crude lipid (4), but was continued on the 48-hour basis to keep the conditions uniform. The chemical determinations were continued a t regular but lengthening intervals throughout the storage period. A final subjective and chemical examination of the 1952 samples was conducted after 2 years of storage. Chemical methods used were described previously (4, 5).

ENZYME ACTION AND OFF‐FLAVOR IN FROZEN PEASa

“…The finding of lowered flavor scores after three months storage is similar to the results obtained with intact raw peas (7). It may be concluded that the addition of enzymes to blanched peas did produce off-flavors ranging in intensity from mild to extremely objectionable.…”

Pea Lipoxidase, Distribution of Enzyme and Substrate in Green Peas

“…THE ENZYME LIPOXIDASE occurs in peas (Siddiqi and Tappel, 1956;Knapp, 1964) and the activity of this enzyme is often said to be responsible for undesirable changes of chlorophyll and flavor (Lee and Wagenknecht, 1951;Wagenknecht et al, 1952 ;Lee et al, 1955 ;Lee, 1956, 1958;Bengtsson and Bosund, 1964).…”

Die Ausschaltung des Fermenteinflusses bei der Gefrierkonservierung von Gemüse 1. Mitt. Der Einfluss der Fermente und Möglichkeiten zur Ausschaltung ihrer Wirkung

“…Geschmacksverschlechterungen waren durch organoleptische Priifungen in unblanchierten Erbsen, Brechbohnen und Mais bereits nach 2-4 Wochen Gefrierlagerung zu erkennen [48]. Analytisch konnte ein Anstieg des Sauregrades der Fettfraktion fur die gleichen Proben schon nach einer Woche festgestellt werden.…”

“…Analytisch konnte ein Anstieg des Sauregrades der Fettfraktion fur die gleichen Proben schon nach einer Woche festgestellt werden. E r vergr6Berte sich mit zunehmender Lagerdauer, hattc jedoch in den ersten Monaten die groBten Zunahmen aufzuweisen [48]. Eine Erhohung des Fettperoxydgehaltes wurde bei Erbsen erstmals nach 3, bei Bohnen nach 4 und beim Zuckermais nach 12 Wochen ermittelt [48].…”

“…E r vergr6Berte sich mit zunehmender Lagerdauer, hattc jedoch in den ersten Monaten die groBten Zunahmen aufzuweisen [48]. Eine Erhohung des Fettperoxydgehaltes wurde bei Erbsen erstmals nach 3, bei Bohnen nach 4 und beim Zuckermais nach 12 Wochen ermittelt [48]. Auch in rohen, gefrorenen Brechbohnen, Spinat und Mais konnten die gleichen Veranderungen des Rohfettes wie bei Erbsen beobachtet werden.…”