Juice, guava

Padula M and Rodriguez-Amaya DB. 1987. Changes in individual carotenoids and vitamin C on processing and storage of guava juice. Acta Aliment 16 209—216. 

International Society for Infectious Diseases (2009). ProMED-mail Trypanosomiasis, food-borne—Venezuela (Vargas), guava juice, 06-APR-2009. Archive number 20090406.1328. Available at http // www.promedmail.org/pis/otn/f p=2400 1202 3498272867640481 NO F2400 P1202 CHECK DISPLAY,F2400 P1202 PUB MAIL ID X,76922. Accessed 25 August 2009. 

Gow, C.Y. and Hsin, T.L. 1999. Changes in volatile flavor components of guava juice with high-pressure treatment and heat processing and during storage. Journal of Agricultural and Food Chemistry 47 2082-2087. 

HIGH PRESSURE AND HEAT TREATMENTS EFFECTS ON PECTIC SUBSTANCES IN GUAVA JUICE... 

The pH adjusted guava juice was poured into a plastic container (volume of about 100 mL) and treated under 1000, 3000, 5000 and 6000 atm pressure for 10 min. The treatment temperature was controlled at 25 °C. 

High Pressure and Heat Treatments Effects on Pectic Substances in Guava Juice... 

The pH adjusted guava juice was pasteurized by thermal treatment at 95 °C for 5 min and was then chilled with ice water to reduce the temperature to below 20°C. The cooled juice was then stored at 4°C until use. 

Guava juice (20 mL) was centrifuged at 800 x g for 10 min. The turbidity of the upper layer solution was estimated by measuring the absorbance at 600 nm using a spectrophotometer, as described by Chandler and Robertson (1983). 

The alcohol insoluble solids (AIS) of the heated, pressurized and untreated guava juice samples were obtained by the procedure proposed by Plat et al (1991). The AIS were fractionated into water soluble pectin (WSP), oxalate soluble pectin (OSP) and alkali soluble pectin (ASP) fractions, according to the procedure given by Dietz and Rouse (1953) and quantified using the carbazole colorimetric method given by Ting and Rouseff (1986). 

The cloud content of guava juice was determined by the method of Klavons et al. (1991). Pulp was removed from all samples by low-speed centrifugation (360 x g for 10 min). The pulpless juice (15 mL) was then centrifuged at 27000 x g for 15 min, to produce a supernatant, the optical density (OD) of which was less than 0.05 at 600 nm. The supernatant was then decanted and the cloud pellet was redissolved in 10 mL of deionized water by vortexing. This process was repeated and the total cloud weight of the sample was obtained by freeze-drying to a constant weight. 

Table 1. Effect of high pressure and heat treatments on changes in the viscosity and turbidity of guava juice ...

Guava juice (30%) was adjusted to pH 3.8 and 12° Brix. Means within a row with different letters are significantly different at 5% level. 

Figure 1 depicts the SEM of cloud substance from guava juice under various processing conditions. The cloud surface of the fresh sample (unheated and not pressurized) was irregular and with unique particle size (Fig. 1, A B). The particle distribution and appearance of pressurized juice (6,000 atm, 25 °C, 15 min) were similar to the fresh sample (Fig. 1, C D). Takahashi et al (1993) have reported that the soluble solid particle distribution in citrus juice does not change after high pressure treatment. However, the cloud surface of pasteurized juice was observed to be greatly different from the pressurized juice (Fig. 1, E F) due to coagulation of the small particles.

Figure 1. SEM pictures of cloud substance is untreated, pressurized and heated guava juice. Guava juice (30%) was adjusted to pH 3.8 and 12°Brix. A, B untreated guava juice. C, D guava juice was pressurized at 6,000 atm and 25 °C for 10 min. E, F guava juice was heated at 95 °C for 5 min.

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