STUDIES ON FROZEN DOUGHS .3. SOME FACTORS INVOLVED IN DOUGH WEAKENINGDURING FROZEN STORAGE AND THAW-FREEZE CYCLES

The mechanism of dough weakening during thaw-freeze cycles and storage in frozen condition was investigated by extensigraphy, protein solubi lity fractionation, and electrophoresis. Molded doughs were frozen and stored for one, seven, or 70 days or subjected to three thaw-freeze ( 3T-F) cycles during seven days of frozen storage. Extensigraph measure ments showed that maximum resistance (R(max)) decreased significantly after one day, after 3T-F cycles, and after 70 days, whereas dough ext ensibility increased significantly only after 70 days of frozen storag e. Extensigraph results for nonfrozen doughs formulated with different yeast levels indicated that the decrease in R(max) during frozen stor age does not appear to be related to the concomitant drop in grassing power. In contrast, a very strong relationship was found between exten sibility and gassing power (r greater-than-or-equal-to -0.95). Therefo re, the substantial decrease in gassing power of the frozen dough stor ed for 70 days appears to be the probable cause of the significant inc rease of extensibility observed for this dough. Reducing sugar content of the doughs after 3T-F cycles was considerably lower than that of d oughs subjected to other storage treatments, indicating that some ferm entation occurred during the thaw part of the thaw-freeze cycle. Small but significant (P < 0.05) increases in the proportion of water-and a cetic-acid-soluble protein fractions were observed for doughs subjecte d to 3T-F cycles. For the dough subjected to 70 days of frozen storage , the proportion of 70% ethanol-soluble protein was significantly high er than for other doughs. Sodium dodecyl sulfate-polyacrylamide gel el ectrophoresis performed under nonreducing conditions clearly showed ch anges in the high molecular weight region (glutenin oligomers) of the electrophoretic pattern of the doughs subjected to the 3T-F cycles. Fa ctors responsible for dough weakening after prolonged frozen storage a nd for dough subjected to repeated thawing and refreezing appear to be different.