Abstract
The aim of this study was to evaluate the stability of color, betaxanthin, and betacyanin pigments in the presence of Cu(II)-dependent hydroxyl radicals (HO•) from ultrasonicated purple cactus pear juice at amplitudes of 40%, 60%, and 80%, in comparison to untreated sample. L* parameter of juice treated at 40% and 80% amplitude for 25 and 15 min, respectively (11.3 and 9.3, respectively), were significantly higher compared to the control; b* and hue parameters of juice treated at 80%, 25 min showed values of 1.7 and 0.1, respectively. Color differences (ΔE) were lower (<3) for juices treated at high amplitude (80%) and short times (3–5 min). Juice treated at 40% 15 min, 60% 25 min, 80% 15 and 25 min presented high values of betacyanins (281.7 mg·L−1, 255.9 mg·L−1, 294.4 mg·L−1, and 276.7 mg·L−1, respectively). Betaxanthin values were higher in the juices treated at 40% 5 min and 80% 15 and 25 min (154.2 mg·L−1, 135.2 mg·L−1, and 128.5 mg·L−1, respectively). Purple cactus pear juice exhibited significant chelating activity of copper ions and great stability when exposed to HO•.
Highlights
Ultrasound is an alternative technology to conventional thermal treatment and is characterized by the generation of longitudinal waves when a sonic wave meets a liquid medium, creating regions of alternating compression and explosion [1]
L* values for juice treated at 40% 25 min and 80% 15 min were significantly higher (11.3 ± 3.8, 9.3 ± 4.2, respectively) than the control, and most other samples which exhibited values between 4.5–8.0
According to Tiwari et al [26], time affects lightness because color pigments in the juice are exposed for longer periods to high shear forces in the vicinity of collapsing bubbles
Summary
Ultrasound is an alternative technology to conventional thermal treatment and is characterized by the generation of longitudinal waves when a sonic wave meets a liquid medium, creating regions of alternating compression and explosion [1]. When high-power ultrasound propagates in the liquid, changes in pressure generate cavitation bubbles that collapse violently in the succeeding compression cycles of a propagated sonic wave. Several mechanisms act when ultrasound is applied to fluids; i.e., bubble implosions that lead to thermal effects or microstreaming, and implosion shock waves that produce mechanical stresses [2] promoting the release of cellular compounds and increase of liquid temperature [3]. Ultrasound technology applied to cactus pear juice has a minimal effect on nutritional quality parameters such as contents of phenols and ascorbic acid or antioxidant activity; ultrasound may even increase the release of some of these compounds [3,4]. Previous studies reported that ultrasound in purple and green cactus pear juices significantly reduces microbial load without affecting its quality and antioxidant parameters [3,4,5,6]
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