Effect of Processing Temperature on Pigments and Color of Spinach^a

Abstract

SUMMARY A method was developed for estimation of chlorophylls a and h, pheophytins a and h, lutein, and carotene in processed spinach. The method, developed primarily for calorimetric studies, involves extraction of the spinach with acetone and chromatographic separation on a sugar‐starch (70:30) column. Equations were developed for spectrophotometric estimation of the amount of each pigment in the eluate from the column. The method gave recovery values of 95–98% for a wide range of pigment mixtures, and a coefficient of variation of approximately 1.5% for reproducibility on the same extract. Fresh spinach was blanched, pureed, packed in glass thermal‐death‐time tubes and processed in an oil bath at 240, 250, 260, 270, and 280°F for a process value equal to Fo 4.9. Color measurements indicated a difference of 4.1 units between the controls and the samples processed at 280°F, and 11.6 units between the controls and the samples processed at 240°F. The pigment changes indicated a progressively smaller change in chlorophylls a and h to pheophytins a and h as the processing temperature was raised. Chlorophyll a was degraded more rapidly than chlorophyll b, and the ratio of the two changed from 1.55 for the samples processed at 280°F, to 0.92 for the samples at 240°F. Some degradation of lutein was observed, particularly at the lower processing temperatures, whereas carotene was unchanged. The pigment‐free tissues also showed more change in color at the lower temperatures, but the contribution of the pigment‐free tissues and the degradation of lutein to the over‐all color change was very small. The major reasons for the change in color of the spinach puree upon processing were, first, the degradation of chlorophyll a to pheophytin a, and second, the degradation of chlorophyll b to pheophytin b.

Chlorophyll Stability During Continuous Aseptic Processing and Storage

“…Only a small quantity of pheophytin a was formed during blanching and no pheophytin b was detected. It is well known from previous reports (Mackinney and Joslyn, 1941;Sweeney and Martin, 19.58;Tan and Francis, 1962;Buckle and Edwards, 1970;Schwartz and von Elbe, 1983) that chlorophyll a is more susceptible to forming pheophytin than chlorophyll b. This was also observed for the continuous processed samples where lower levels (calculated from blanched samples) of chlorophyll b were converted to pheophytin relative to chlorophyll u (Table 1).…”

Combined Effect of Drying Time and Slice Thickness on the Solar Drying of Okra

“…No signiÐcant di †er-ence (P \ 0É05) in green colour between the three samples was observed after 48 h of drying. Figure 6(B) which reÑects the trend in visual lightness or whiteness (L* values), showed a general decrease during the Ðrst 48 h of drying followed by an increase after 48 h. The decreasing trend was due to enzymatic browning occurring at the cut surfaces of the samples (PenÐeld and Campbell 1990), as well as possibly the degradation of chlorophyll to olive-brown pheophytins (Gold and Weckel 1959 ;Tan and Francis 1962), resulting in darkening and hence the decrease in L* values. The increasing trend after 48 h may be due to the fact that, with increasing dryness, browning becomes less severe after it has reached a maximum at 48 h (intermediate moisture content of 122É1È 211É3 g kg~1) resulting in higher L* values.…”

Thermal Degradation Kinetics of Chlorophyll in Pureed Coriander Leaves

“…Others have attempted to retard the formation of pheophytin and preserve the color by pH control (Clydesdale and Francis 1968) by minimizing heat exposure by applying HTST (Tan and Francis 1962), or by combining HTST with pH adjustments (Gupte and Francis 1964;Clydesdale et al 1970). The major finding of these studies is that both pigment and visual color degradation during thermal processing follows the first-order reaction kinetics.…”