Impact of Thermal Treatment and Storage on Color of Yellow‐Orange Cactus Pear (Opuntia ficus‐indica[L.] Mill. cv. ‘Gialla’) Juices

Abstract

The impact of heating at 75, 85, and 95 • C during 60 min on overall color and betalain retention of yellow-orange cactus pear (Opuntia ficus-indica [L.] Mill. cv. 'Gialla') juice after a 24-h color regeneration period was investigated. The addition of 0.1% isoascorbic acid prior to heating minimized color alteration as well as betalain degradation to a significant level. A correlation between the total betaxanthin retention and the indicaxanthin/isoindicaxanthin ratio was detected in heated juice samples, thus proving the indicaxanthin/isoindicaxanthin ratio as a valuable indicator of thermally treated cactus pear juices. Notably, the same ratio was instrumental for retrospectively calculating the initial betaxanthin content. Additionally, storage experiments over a period of 6 mo were conducted. Samples kept in the dark exhibited notably better color and pigment retentions as compared to illuminated samples. A significantly stabilizing effect was also observed in samples with isoascorbic acid fortification. While indicaxanthin and betanin were predominantly degraded through hydrolytic cleavage upon both heat exposure and storage, isomerization was only marginal for betanin. In contrast, 2-decarboxy-betanin formation was exclusively found for nonfortified heated samples while decarboxylated indicaxanthin could not be detected. Thermal treatment and pigment regenerationAliquots of 20 mL cactus pear juice (pH 4) with and without addition of 0.1% isoascorbic acid were heated in a water bath at 75, 85, and 95 • C under continuous stirring in a 100-mL round-neck glass sealed with a rubber stopper for 5, 10, 15, 30, 45, and 60 min, respectively. Immediately after heating, samples were cooled in an ice bath for 90 s to stop further degradation. Following a period

Comparative Thermal Degradation Patterns of Natural Yellow Colorants Used in Foods

“…In an intermediate position were curcumin, gardenia yellow and riboflavin, with remaining absorbances after 6 h at 90°C, of 83, 67 and 53 %, respectively. In the Opuntia extract, only 11 % of its initial absorbance remained after this thermal treatment, revealing the low stability of betaxanthins at higher temperatures, as reported previously in the bibliography [17]. At 30, 50 and 70°C, also ß-carotene and lutein were the colorants showing the highest stability, followed by curcumin, gardenia yellow, riboflavin and Opuntia betaxanthins (Fig.…”

“…The CIEL*a*b* system is a versatile and reliable method to appraise precise color modifications and is extensively used for routine quality control measurements by food manufacturers [17]. In agreement with previous studies, thermal processing involved a slight increase in lightness (L*) [15,24], although more profound modifications could be observed in the colorimetric plane.…”

“…As temperature was higher the different stability between carotenoids and curcumin, riboflavin, gardenia yellow and betaxanthins became much more evident. In previous studies, high half-life values were also reported for carotenoids whereas the low half-life values of betaxanthins at temperatures higher than 30°C is well documented [17,19].…”

“…Also CIEL*a*b* color space represent a versatile tool commonly used to monitor color properties [17]. The initial solutions of the six natural yellow colorants used in this investigation were characterized monitoring their spectral properties and CIEL*a*b* parameters.…”

Effects of gamma irradiation on bio-chemical and physico-chemical parameters of fresh-cut red beet (Beta vulgaris L. var. conditiva) root

“…The juice obtained was used for betalain spectrophotometric quantification according to Mobhammer et al (2006) by using UV-mini-1240UV-VIS spectrophotometer (Shimadzu Corporation, Kyoto, Japan). Briefly, the evaluation of betacyanin (as betanin equivalents) or betaxanthin (as vulgaraxanthin equivalents) content was performed by diluting the juice with a McIlvaine buffer (pH 6.3), until the absorbances measured at 536 and 476 nm did not surpass a value of 1.00 (±0.05).…”