Solomat Mpm 500e Manual
U.-Technol., 29, 708–713 (1996)Minimally Processed Pomegranate Seeds Maria I. Gil., Juan A. Mart´ınez and Francisco Artes ´ Postharvest and Refrigeration Laboratory, Food Science and Technology Department, CEBAS (CSIC), PO Box 4195, Murcia 30080 (Spain) (Received March 3, 1995; accepted January 4, 1996)Ready-to-eat pomegranate seeds were prepared and their quality attributes and appearance was followed during storage for 7 d under different conditions.
Quality attributes, titratable acidity, total soluble solids, L. values, absorbance at 510 nm (anthocyanin content) and absorbance at 446 nm (brown metabolites) were analysed. Respiratory activity, appearance of the seeds (shriveling and browning), and weight loss were also evaluated. The influence of different washing treatments, storage temperatures (8, 4 and 1 °C) and actively or passively modified atmosphere packaging on the quality of the minimally processed pomegranate seeds was studied. Washing the seeds with chlorine and chlorine followed by ascorbic and citric acid were selected, and storage at 1 °C led to the best quality preservation.
Solomat Mpm 500e Manual
The best overall results were obtained for seeds washed with chlorine (100 mg/kg) plus antioxidants (5 g/L ascorbic acid and 5 g/L citric acid), and sealed in oriented polypropylene film using an initial atmosphere actively modified to 20 mL/L O2 and 0 mL/L CO2. Under these conditions, minimally processed pomegranate seeds maintained good quality and appearance for 7 d of storage at 1 °C without fungal attacks or off-flavour development. ©1996 Academic Press LimitedIntroduction Pomegranate is the fruit of Punica granatum L.
Particle
(Punicaceae) which is widely grown in Mediterranean countries, and has been introduced to most parts of the tropics and subtropics (1). The seeds are the edible part of the fruit which are normally consumed fresh. One of the main features of its quality is the red colour of both its seeds and juice (2–4). However, pomegranate consumption is limited due to difficulties in peeling to obtain the seeds.
Therefore, production of pomegranate seeds in ‘ready-to-eat’ form would be a convenient and desirable alternative to the consumption of fresh fruits and may increase pomegranate demand by consumers. Minimally processed pomegranate seeds have a greatly reduced post-harvest life compared to whole fruit. Modified atmosphere packaging (MAP) may be an excellent method of extending shelf-life of pomegranate seeds (3).
To prevent microbial development, washing lightly processed products with chlorine solutions has proven essential (5). In pigmented products, an additional problem is the discolouration caused by oxidation of phenolic pigments and other phenolic compounds catalysed by phenolases or peroxidases (6). Since the colour of pomegranate seeds is the most important quality attribute for consumers, its stability must be preserved (4).
Washing with antioxidant solutions might therefore prove useful. Selected conditions for pomegranate seed preparation have been described (7).To whom correspondence should be addressed.0023-6408 + 06$25.00/0but little work on minimally processed pomegranate seeds has been published so far. The purpose of this work was the preparation of pomegranate seeds and the study of the effect of storage temperature, pretreatments and MAP technique on the keeping quality of this product.Materials and Methods Plant material Pomegranates (cv. Mollar) were harvested (October 3, 1994) in the typical production area of Elche (Alicante, Spain), located at the Mediterranean coast, and transported 60 km the same day by car to the laboratory and kept at 5 °C until used the next day.
Ventilation
Seeds were obtained by manual peeling under refrigerated conditions (13 °C).Washing treatments Six different washing treatments were tested including distilled water, chlorinated water and solutions of ascorbic and/or citric acids with and without chlorine. Concentrations and rinsing times are shown in Table 1. Seeds were divided into uniform groups (250 g) and each was dipped in 5 L of appropriate solution.
Washing treatments were carried out at 13 °C. After the rinsing time indicated for each experiment (Table 1), seeds were dried in a manual spin-dryer for 1 min and placed at 1 °C for 1 h to remove residual water before analysis. ©1996 Academic Press Limited708lwt/vol. 29 (1996) No.
8Table 1 Washing treatments Washing Water Chlorine (100 mg/kg) Ascorbic acid (5 g/L) Citric acid (10 g/L) Ascorbic acid (5 g/L)+citric acid (5 g/L) Chlorine (100 mg/kg)+ ascorbic acid (5 g/L)+citric acid (5 g/L)Rinsing time 5 min 5 min 30 s 30 s 30 s 5 min 30 sStorage conditions Packaged and unpackaged seeds were stored for 7 d at different temperatures (8, 4 and 1 °C) to select the best storage conditions. Relative humidity was 90 ± 5% controlled by a humidostat (cen-frio, Spain) and measured by a thermo-hygrometer (Solomat, mod. MPM 500e, U.K.) for all treatments. The storage period of 7 d was considered adequate as a retail sale period. After peeling, seeds were divided into two batches. One batch was dipped in chlorine (100 mg/kg) for 5 min and the other batch was first dipped in chlorine (100 mg/kg) for 5 min followed by dipping for 30 s in a solution of ascorbic acid (5 g/L) and citric acid (5 g/L).
Seeds were dried as described above. For experiments with unpackaged seeds, 50 g were placed in open plastic trays (9 cm diameter and 1 cm thick). In addition, 50 g of seeds were placed in heat-sealed pouches (9 3 12 cm) made of oriented polypropylene (OPP) film of 40 µm thickness (Derfilm 40 DF 300, Derprosa, Spain), with an O2 permeability of 290 mL/m2 24 h bar, a CO2 permeability of 1112 mL/m2 24 h bar, and a water vapour transmission rate of 0.090 g/m2 24 h (all values at 83% RH and 5 °C). Handling was carried out at 13 °C.MAP treatments To study the effect of MAP treatments, seeds were washed and handled as in the storage study and then packaged in sealed OPP pouches with the characteristics described above, and perforated oriented polypropylene film (POPP) (33 holes of 2 mm per dm2) which allowed a free diffusion of gases, as a control. A modified atmosphere was passively established within each heat-sealed pouch (9 3 12 cm) as a consequence of both the respiration of the seeds and the permeability of the film. Storage conditions were 1 °C and 90 ± 5% RH for 7 d.
Initial gas concentrations (140 mL/L O2 and 80 mL/L CO2 for the CO2 treatment and 20 mL/L O2 and 0 mL/ L CO2 for the N2 treatment) were established by active modification, by flushing a specific gas in a gas exchange device with a vacuum packaging machine Egarvac and protective mixing gas KM 100-3M. Changes in concentrations of O2 and CO2 within the packages were monitored daily using a Perkin Elmer Autosystem gas chromatograph equipped with a thermal conductivity detector (TCD).Analytical evaluation Quality attribute measurements were carried out on the juice obtained by squeezing 50 g of seeds with a commercial turmix blender (Moulinex). Titratable acidity (TA) was determiend by titrating juice samples with 0.1 mol/L NaOH (8) and was expressed as g of citric acid/100 mL. Total soluble solids (TSS) was measured with an Atago N1 refractometer (refractometric reading at 20 °C) and expressed in °Brix. Colour components L., a.
and b. were measured with a tristimulus colorimeter (Chroma Meter CR-300, Minolta) using a liquid sample holder CR-A70 (Minolta) where 35 mL of juice were analysed. Two millilitres of juice were centrifuged in an Eppendorf centrifuge at 1200 3 g for 2 min and the anthocyanin content and browning compounds were measured at 510 nm and 446 nm, respectively, using a Pye-Unicam SP-8-100 spectrophotometer. Respiratory activity The respiration rate (RR) was determined by the Gas Stream Method (9), placing 50 g of seeds into a 100 mL gas-tight glass jar at 20 °C and using 0.2 L/min continuous flow of humidified air (above 95% RH) free of CO2. The increase in CO2 content in the head space over a fixed period of time (60 min) was measured. CO2 emissions were determined using a gas chromatograph Hewlett Packard 5370 A model, equipped with a Porapack-Q column and a thermal conductivity detector (TCD).
Results were expressed as mL CO2/kg/h. Helium was used as carried gas. Sensory evaluation The subjective quality of minimally processed pomegranate seeds after the different treatments was assessed by a panel of five trained judges (10). Two women and three men were instructed to judge appearance (browning, shriveling, skin defects) and visual fungal attacks. Statistical analysis Five replicates of each treatment were examined.
Data were analysed by analysis of variance (P.