| Summary: | 碩士 === 國立屏東科技大學 === 熱帶農業暨國際合作研究所 === 93 === The tropical fruits are adequate for the increasing market of fruit juices and based fruit drinks by their diversity of aromas and flavours and by their nutritional value. In such group, acerola (Malpighia emarginata, DC.) appears as potentially attractive due especially to its high ascorbic acid content, its attractive red color, and its antioxidant capacity.
The main objective of this work was to develop processes for obtaining concentrated acerola juice, maintaining its main nutritional and sensory characteristics during processing and storage.
For achieving the goal of this study, the potential of two concentration techniques (rotary and boiling evaporation) was evaluated. Fruits used for the juice processing were divided into two parts depended on whether or not the blanching technique was applied. At the end of the concentration processes, four (4) products were obtained namely, rotary concentration non-blanching (RCNB), rotary concentration blanching (RCB), boiling concentration non-blanching (BCNB), and boiling concentration blanching (BCB). Immediately after processing (zero storage time), the products were chemically evaluated using two markers: color quality parameters (Hunter a b values, anthocyanin degradation index, and color density) and vitamin C content. The product that exhibited the best color quality parameter and the highest vitamin C content was selected and stored under different conditions (25oC with light, 25oC with dark, and 4oC) for 5 months. The follow-up of the concentrate during the storage period was performed using several markers including: color quality parameters (absorbance at 510 nm, chroma value, color density, anthocyanin degradation index and total free anthocyanin content), vitamin C, flavonoids and phenolic acid profiles, furfural, and antioxidant capacity.
Results showed that at zero storage time, the RCNB samples exhibited higher red color intensity (a value), higher color density, lower anthocyanin degradation index (DI) and lower yellow color intensity (b value). On the other hand, by comparison with the vitamin C content of the fresh acerola juice, loss of vitamin C was observed in both processes. Compared to the fresh juice, losses of 7.57%, 13.54%, 20.11%, and 45.50% vitamin C were observed for RCNB, RCB, BCNB, and BCB respectively. Thus, the RCNB samples were chosen and stored under the three storage conditions mentioned above. During storage, the absorbance at 510 nm (red color), the chroma value and the color density decreased from one to three months of storage and increase thereafter, while the free anthocyanin content and the anthocyanin degradation index decreased during the whole storage period, suggesting that the observed increased in the absorbance at 510 nm after three months was probably not due to the presence of anthocyanin itself. On the other hand, the vitamin C content, the FRAP decreased, while the DPPH scavenging activity and the ferrous ion chelating power increased over time. After 5 months of storage at 25oC with light, 25oC with dark, or 4oC; vitamin C degradation rates of 3.85%, 3.07%, and 1.66 % per week were respectively observed. Chlorogenic acid, caffeic acid, and quercetin represented the main non-anthocyanin phenolic compounds in acerola fresh juice and concentrates. Statistically, significant correlation coefficients were found between vitamin C and anthocyanin suggesting a possible interaction between the two compounds in the system. On the other hand, in the early stage of the storage, positive correlation was found among ferric reducing ability of plasma (FRAP), vitamin C, and anthocyanin content suggesting that anthocyanin and vitamin C are probably the main source of reducing power of acerola products at this stage of the storage. High positive correlation was found among the browning index (expressed by the absorbance at 420 nm), DPPH scavenging ability, ferrous ion chelating ability, total phenolic content and DPPH, suggesting that the antioxidant capacity of the concentrates in the later stage of the storage might be conjointly due to browning compounds and non-anthocyanin phenolics.
As conclusion, at zero storage time, the rotary concentration technique was proved to be better than the boiling one. During storage, important losses of vitamin C and red color occurred. The reducing power of the products decreased with the increasing of the storage time, while the free radical scavenging ability (DPPH) and the ferrous ion chelating power increased over time. Samples stored at 4oC maintained better characteristics of the fresh juice.
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