Gustavo Martínez

Quality of heat-treated strawberry fruit during refrigerated storage

Strawberries cv. Selva were heat-treated in an air oven (45 °C, 3 h) and then stored at 0 °C for 0, 7 or 14 days. Afterward, fruits were placed at 20 °C and monitored after 24, 48 or 96 h and the effect of heat treatment on the following parameters was recorded: weight loss, external color, anthocyanin content, firmness, titratable acidity, total and reducing sugars, fruit decay and count of colony forming units (CFUs) for bacteria and molds. Heat-treated fruits showed higher hue angle than controls, indicating the delay of red color development. The treatment diminished fruit lightness (L*), although the effect reverted during holding at 20 or at 0 °C. The application of the treatment caused an initial weight loss close to 2% but afterwards, heat-treated fruits showed lower weight loss rate at 20 °C. Heat-treated fruits had lower acidity than controls, but there was no difference in the content of total sugars between control and treated fruits. Heated fruits were slightly firmer at the end of the treatment, and they softened less than controls after 24 h at 20 °C. Heat-treated fruits remained firmer than controls after 7 days of cold storage, and the relative difference in softening persisted after 48 h at 20 °C. However, no difference in treated and control fruit firmness was observed after 14 days of storage at 0 °C and following 48 h at 20 °C. In the absence of storage, heat-treated fruits showed lower decay at 20 °C than controls. After 7 days at 0 °C followed by 72 h at 20 °C, the percentage of decayed fruits was lower in heat-treated than in control fruits. The treatment decreased the initial bacterial population, but did not modify the amount of mold initially present. After 7 days of cold storage, the CFU number for bacteria were lower in treated than in control fruits. This difference was still significant after 48 h at 20 °C. In the case of molds, heat-treated fruits that were stored for 7 or 14 days at 0 °C and then transferred to 20 °C for 48 h showed lower CFU value than controls.

Polyphenoloxidase activity from strawberry fruit (Fragaria ananassa, Duch., cv Selva): characterisation and partial purification

In this work, polyphenoloxidase (PPO) from Selva strawberry fruit (Fragaria × ananassa, Duch) was extracted, characterised and partially purified. The activity of PPO was analysed in crude extracts obtained from either fresh fruits or acetone powder. The presence of NaCl and Triton X-100 in the extraction buffer caused a marked increase in enzyme extractability. The enzyme showed an apparent Km value of 11.2 mM with pyrocatechol as substrate. The maximum enzyme activity was observed at 50 °C and pH 5.3–6.0 without SDS and pH 7.2 in the presence of SDS. The presence of SDS increased PPO activity at pH 7.2 but diminished it at pH 6.0. The enzyme showed high thermal stability and maintained activities equal to or greater than 50% of its maximum activity in the 2.6–9.3 pH range. One polyphenoloxidase isoenzyme was detected in crude extracts of all ripening stages, showing an isoelectric point of 7.3. The specific activity of PPO decreased continuously through fruit ripening. Maximum specific activities were found at the ‘small green’ and ‘large green’ ripening stages. A total enzyme extract was partially purified by means of (NH4)2SO4 precipitation and cationic exchange chromatography in an FPLC system. The purification grade achieved was near 25. The partially purified enzyme showed an isoelectric point equal to 7.3 and a molecular mass of 135 ± 4 kDa for the native protein. © 2000 Society of Chemical Industry

A fruit-specific plasma membrane aquaporin subtype PIP1;1 is regulated during strawberry (Fragaria × ananassa) fruit ripening

Despite the advances in the physiology of fruit ripening, the role and contribution of water pathways are still barely considered. Our aim was therefore to characterize aquaporins, proteins that render the molecular basis for putative regulatory mechanisms in water transport. We focused our work on strawberry (Fragaria xananassa) fruit, a non-climacteric fruit of special interest because of its forced brief commercial shelf life. A full-length cDNA was isolated with high homology with plasma membrane (PM) intrinsic proteins (named FaPIP1;1), showing a profile with high expression in fruit, less in ovaries and no detection at all in other parts. Its cellular localization was confirmed at the PM. As reported in other plasma membrane intrinsic proteins subtype 1 (PIP1s), when expressing the protein in Xenopus leavis oocytes, FaPIP1;1 shows low water permeability values that only increased when it is coexpressed with a plasma membrane intrinsic protein subtype 2. Northern blotting using total RNA shows that its expression increases during fruit ripening. Moreover, functional characterization of isolated PM vesicles from red stage fruit unequivocally demonstrates the presence of active water channels, i.e. high water permeability values and a low Arrhenius activation energy, both evidences of water transport mediated by proteins. Interestingly, as many ripening-related strawberry genes, the expression pattern of FaPIP1;1 was also repressed by the presence of auxins. We therefore report a fruit specific PIP1 aquaporin with an accumulation pattern tightly associated to auxins and to the ripening process that might be responsible for increasing water permeability at the level of the PM in ripe fruit.

Characterization of peroxidase-mediated chlorophyll bleaching in strawberry fruit

Peroxidase (POX) from strawberry fruits was analyzed for its capacity to bleach chlorophyll. The partially purified enzyme preperation catalyzed the bleaching of chlorophylls and their derivatives in the presence of H(2)O(2) and phenolic compounds. The optimal reaction conditions were 35 degrees C, pH 5.2 and ionic strength equal to 0.2. The maximum activity was observed at 1 mM of H(2)O(2), while higher concentrations inhibited enzyme activity. Compounds with a high affinity to the heme group, radical scavengers and reducing agents, showed an inhibitory effect. Phenolic compounds such as umbelliferone, naringenin and p-substituted monophenols acted as cofactors. Instead, other phenolic compounds tested such as caffeic acid, catechin, ellagic acid, esculin and quercetin inhibited the activity of POX on chlorophylls. Phenolic compounds extracted from strawberry fruits showed an inhibitory effect on POX-chlorophyll bleaching activity, although this effect decreased markedly during ripening. POX showed higher affinity for compounds derived from chlorophyll a than from chlorophyll b, and the enzyme preferentially degraded chlorophyll derivatives with the Mg(2+) ion present and the phytol group removed. The POX-chlorophyll bleaching activity was found in all ripening stages from small green to ripe, the highest activity corresponding to large green fruits.

Cloning, functional characterization, and co-expression studies of a novel aquaporin (FaPIP2;1) of strawberry fruit

In strawberry, the putative participation of aquaporins should be considered during fruit ripening. Furthermore, the availability of different firmness cultivars in this non-climacteric fruit is a very useful tool to determine their involvement in softening. In a previous work, the cloning of a strawberry fruit-specific aquaporin, FaPIP1;1, which showed an expression profile associated with fruit ripening was reported. Here, FaPIP2;1, an aquaporin subtype of PIP2 was cloned and its functional characterization in Xenopus oocytes determined. The FaPIP2;1 gene encodes a water channel with high water permeability (Pf) that is regulated by cytosolic pH. Interestingly, the co-expression of both FaPIP subtypes resulted in an enhancement of water permeability, showing Pf values that exceeds their individual contribution. The expression pattern of both aquaporin subtypes in two cultivars with contrasting fruit firmness showed that the firmer cultivar (Camarosa) has a higher accumulation of FaPIP1 and FaPIP2 mRNAs during fruit ripening when compared with the softer cultivar (Toyonoka). In conclusion, not only FaPIP aquaporins showed an expression pattern associated with fruit firmness but it was also shown that the enhancement of water transfer through the plasma membrane is coupled to the presence/absence of the co-expression of both subtypes.

β-Xylosidase in strawberry fruit: Isolation of a full-length gene and analysis of its expression and enzymatic activity in cultivars with contrasting firmness

Strawberry is a non-climateric fleshy fruit, which softens quickly and has short post-harvest life. Ripening is associated with an increment of pectin solubility and a reduction of the content of hemicelluloses. In this work, we have cloned the full-length cDNA encoding a β-xylosidase (FaXyl1) from Fragaria×ananassa and we have characterized its expression in two strawberry cultivars with contrasting fruit firmness. The analysis of the predicted protein showed that FaXyl1 is closely related to other β-xylosidases from higher plants. The recombinant protein obtained by over-expressing FaXyl1 in Escherichia coli had β-xylosidase activity against the artificial substrate p-nitrophenyl β-d-xilopyranoside. Differently from other bifunctional xylosidases, no α-l-arabinofuranosidase activity was detected in the recombinant enzyme. The expression of FaXyl1 gene was analyzed by northern-blot in Camarosa and Toyonaka strawberry cultivars, and compared with the corresponding protein data obtained by Western-blot and with the β-xylosidase activity during ripening. The softest cultivar (Toyonaka) showed an early accumulation of FaXyl1 transcript and a higher expression of the corresponding protein during ripening, which correlates with a higher β-xylosidase activity in all ripening stages analyzed.

‘Fish-tail’ projectile points and megamammals: new evidence from Paso Otero 5 (Argentina)

The Paso Otero 5 site is located in the middle basin of the Quequen Grande river (Buenos Aires Province, Argentina). This site is the first recorded Pleistocene-Holocene archaeological context in the grasslands of the Interserrana Bonaerense Area at which extinct megamammals and a ‘fish-tail’ projectile point have been recovered in association from buried soil dated to c. 10,200–10,450 BP.

Maintenance of fresh boysenberry fruit quality with UV-C light and heat treatments combined with low storage temperature

Summary Mature boysenberries (Rubus hybrid) were harvested, heat-treated (45°C for 1 or 3 h or 47°C for 1 h) or exposed to UV-C light (2.3, 4.6 or 9.2 kJ m–2), and stored at 20°C for 2 d. Fruit treated with 9.2 kJ m–2 or 45°C for 1 h showed less damaged drupelets per fruit and/or remained firmer than untreated fruit after 2 d. Those treatments were selected for further analyses. In another experiment, boysenberries were either UV-C (9.2 kJ m–2) or heat-treated (45°C for 1 h) and stored either at 20°C for 1 d or at 0°C for 4 d before transfer to 20°C for 1 d. Both UV-C and heat treatments reduced softening and/or fruit damage. Treated fruit had lower respiration rates and anthocyanin leakage than control fruit suggesting greater tissue integrity. Titratable acidity, pH, total sugar content and antioxidant activity in treated fruit showed fewer changes than in control fruit when stored at 20°C for 1 d. Results suggest that heat or UV-C treatment, alone or in combination with refrigerated storage, may be a useful non-chemical mean of maintaining boysenberry fruit quality and extending postharvest life.

Paleosols on Late Cainozoic loessic sequences in the northeastern side of Tandilia Range, buenos aires, Argentina

Abstract The purpose of this work is to describe and characterize paleosols from Late Cainozoic loessic sequences in the northeastern flank of Tandilia Range. Pedological and non-pedological levels are described, considering the vertical (thickness, color, texture and structure) and horizontal (lateral pattern) development. Mineralogical, grain size, physico-chemical features are analyzed in type profiles. This study recognizes two groups of paleosols associated with distinct paleoenvironmental conditions: (I) paleosols which are regionally continuous and extensive, related to moisture conditions wetter than the present ones, showing truncated and superimposed profiles; (II) paleosols related to water bodies, showing uneven distribution which are mainly topographically controlled. Sediments that have undergone pedogenesis are identified by their morphological, physico-chemical, textural and mineralogical characteristics and bioturbation features. The history of pedogenesis and erosion is related to the alternating humid-arid climatic cycles, that have affected the region since the Plio-Pleistocene, to the present.

IMPLICACIONES PALEOAMBIENTALES DE LA PRESENCIA DEL GÉNERO CERATOPHRYS (ANURA, CERATOPHRYINAE) EN CONTEXTOS ARQUEOLÓGICOS DE LA TRANSICIÓN PAMPEANO-PATAGÓNICA EN EL HOLOCENO TARDÍO (CURSO INFERIOR DEL RÍO COLORADO, ARGENTINA)

In this work, we report the presence of the Ceratophrys genus at the archaeological locality of San Antonio and at the Paso Alsina 1 archaeological site, situated at the lower basin of the Colorado river (Buenos Aires province, Argentina). The materials communicated here are assigned to the late *