Effects of pre‐freezing,puree content and pasteurisation regime on colour stability of strawberry nectar made from puree

BACKGROUND: Heat treatment during processing of strawberry products has been proposed to negatively affect colour stability. Moreover, the role of enzymes with respect to colour stability is ambiguous when consulting the existing literature. The aim of the present study was to investigate the impact of various processing parameters (pre‐freezing, puree content, pasteurisation temperature and heating time) on the colour stability and anthocyanin monomer and L ‐ascorbic acid contents of strawberry nectars made from puree. In addition, the effect of different enzyme activities on colour stability during storage of strawberry nectars was investigated. RESULTS: Pre‐freezing of strawberries before processing had a significant positive effect on the colour stability of nectars made from puree. No significant effect on colour stability was found for higher puree contents. Increasing both the pasteurisation temperature and the heating time had a significant positive effect on colour stability. Results showed that colour degradation during storage was mainly due to residual enzyme activities. The shelf‐life of strawberry nectar could be extended about fivefold by adding an enzyme inhibitor. CONCLUSION: The colour stability of strawberry nectar made from fresh puree may be improved to some extent by an appropriate pasteurisation regime. Enzymes play an important role in colour degradation during storage of the nectar. Inactivation of these enzyme activities, however, could not be achieved even after a heat treatment at 90 °C for 60 min. Copyright © 2008 Society of Chemical Industry     

Comparison of high pressure treatment and thermal pasteurization effects on the quality and shelf life of guava puree

The effects of high pressures and thermal pasteurization on the survival of microorganisms, enzyme inactivation and quality changes of guava puree during storage at 4°C were investigated and compared with untreated samples. After treatment at a pressure of 600MPa and 25°C for 15 min, the microorganisms in guava puree were inactivated to less than 10 cfu mL⁻¹ and the product exhibited no change in colour, pectin, cloud and ascorbic acid content as compared with fresh samples. The inactivation of enzymes in guava puree by thermal pasteurization was greater than by high pressures. The microbial count in guava puree reduced to 200 cfu mL⁻¹ and the product showed marked changes in viscosity, turbidity and colour when heated at 88–90°C for 24s. The content of pectin, cloud and ascorbic acid as well as colour in untreated and high pressurized (400MPa) guava puree gradually decreased, whereas these changes were not observed in pasteurized (88–90°C) and high pressurized (6000MPa) puree during storage at 4°C for 60 days. The guava puree treated at 600MPa and 25°C for 15 min retained good quality similar to the freshly extracted puree after storage at 4°C for 40 days.     

The study of phenolic profiles of raw apricots and apples and their purees by HPLC for the evaluation of apricot nectars and jams authenticity

The possibility of proving the authenticity of apricot nectars and jams has been investigated by using the phenol compound fingerprint. Phenol composition of the raw material (apricots and apples), their purees, apricot nectars and jams (with and without addition the definite shares of apple puree) prepared under laboratory conditions and commercial apricot nectars and jams has been determined by high performance liquid chromatography with the UV-Diode Array detection.In addition to large number of various phenol compounds contained in an apples, characteristic marker compounds of the dihydrochalcone group (phloretin 2′-xylosylglucoside and phloretin 2′-glucoside), could be determined. By using the mentioned compounds, undeclared apple admixture in the apricot based products could be detected. The cheaper admixture of the apple puree (⩾10%) in the apricot nectars could be proved by using phloretin 2′-glucoside and phloretin 2′-xylosyglucoside, and only by using phloretin 2′-glucoside if apple puree was added in relatively low level about 5%. The undeclared admixture of apple puree in apricot jams could be detected by both mentioned dihydrochalcones if apple puree was added in level above 20%, and only by phloretin 2′-glucoside if apple puree was added in level about 10%.     

OPTIMIZATION OF GUAVA JUICE AND POWDER PRODUCTION

Enzyme treatment of guava puree was optimized for yield and clarity by first determining the most effective concentration, then varying both incubation time and temperature. Application of Pectinex Ultra SP-L® was optimal using 700 ppm enzyme for 1.5 h at 50C. Clarified guava juice was clearer (89.6%) when prepared using ultrafiltration (MW cut-off 40–60 kDa) rather than plate and frame filtration (82.8%); however, the latter was higher in both soluble solids and ascorbic acid. Clarified guava juice powders were made using freeze-drying, spray drying and tunnel drying. The freeze-dried product had superior quality; however, the spray-dried product was stable and may be more economical. Sensory panelists ranked the cloudy juice prepared from aseptic guava puree highest, and there were no significant differences between the juices from pasteurized, clear nectar, freeze-dried puree powder or juice powder.     

Lipochromes,vitamins, aromas and other components of virgin olive oil are affected by processing technology

A stone mill-integral decanter (SD) olive processing line was compared with a traditional stone mill-press (SP) line, a discontinuous method, that, if properly used, yields high-quality virgin olive oils. With “difficult olives” (not easy to process), the SD line yielded oils characterised by: (1) higher contents of pleasant volatiles, tocopherols, β-carotene, xanthophylls, chlorophylls, pheophytins and waxes; (2) higher values of the 1,2-diglycerides/1,3-diglycerides ratio, integral colour index and chroma; (3) lower contents of phenols, secoiridoids, unpleasant volatiles, aliphatic alcohols, triterpene alcohols and sterols; and (4) lower values of turbidity, brightness and oxidative stability. With “non-difficult olives” (easy to process), whose paste needed to be fluidised with lukewarm water, the SD line yielded oils showing higher contents of pleasant volatiles and tocopherols, lower contents of unpleasant volatiles and comparable contents of phenols and lipochromes. The content of organophosphorus pesticide residues did not depend on the processing method.     

Volatile Composition and Aroma Activity of Guava Puree Before and After Thermal and Dense Phase Carbon Dioxide Treatments

Volatiles from initially frozen, dense phase carbon dioxide (DPCD)‐ and thermally treated guava purees were isolated by solid phase microextraction (SPME), chromatographically separated and identified using a combination of gas chromatography‐mass spectrometry (GC‐MS), GC‐olfactometry (GC‐O), and GC‐pulsed flame photometric detector (GC‐PFPD, sulfur mode). Fifty‐eight volatiles were identified using GC‐MS consisting of: 6 aldehydes, 2 acids, 15 alcohols, 6 ketones, 21 esters, and 8 terpenes. Eleven volatiles were newly identified in guava puree. Hexanal was the most abundant volatile in all 3 types of guava puree. Ten sulfur compounds were identified using GC‐PFPD of which 3 possessed aroma activity and 3 were not previously reported in guava puree. Both treatments profoundly reduced total sulfur peak areas and produced different peak patterns compared to control. Thermal treatment reduced total sulfur peak area 47.9% compared to a loss of 34.7% with DPCD treatment. Twenty‐six volatiles possessed aroma activity. (Z)‐3‐Hexenyl hexanoate was the major contributor to the aroma of the freshly thawed and DPCD‐treated guava puree. DPCD treatment reduced total MS ion chromatogram (MS TIC) peak area 35% but produced a GC‐O aroma profile very similar to control. Whereas thermal treatment reduced total TIC peak area only 8.7% compared to control but produced a 35% loss in total GC‐O peak intensities.     

Chlorophyll, colour and pH changes in H.T.S.T. processed green pea puree

Summary. Pea puree of pH 6.95 and pH 8.45 was heat processed in thermal death-time tubes at temperatures between 115.6°C and 148.9°C to a process value of F₀= 6.0. Chlorophyll pigments, Hunterlab colour indices and pH were determined before and after high temperature-short time (H.T.S.T.) processing and during storage for 18 months at 20°C, 2.8°C, and −23.3°C.
Highly significant correlations were found between per cent conversion of chlorophylls to pheophytins and objective colour indices derived from tristimulus measurements on stored pea puree. the degree of chlorophyll conversion, and hence puree colour, were both markedly affected by process temperature, product pH, storage time and storage temperature, but long-term storage stability was achieved only by combinations of two or more variables.
Changes in pH of processed and stored puree were directly related to changes in pigments and colour, and it appears that pH control during processing and storage offers the most likely means of colour and pigment retention in heat processed chlorophyll-containing foods.     

Effect of packaging materials and storage temperature on the quality of sour cherry nectar

The purpose of this research was to determine the effects of the packaging materials and size on the stability of monomeric anthocyanins, polyphenols, antioxidant activity, ascorbic acid, colour index and hydroxyl methyl furfural (HMF) during the 12‐month shelf life of sour cherry nectars at 4 °C and 20 °C. Sour cherry nectars were aseptically filled out into packaging of different sizes and materials. The packaging included cartons of two different sizes (200 and 1000 mL) and aluminium cans (330 mL). Results showed that the nectars were of better quality when stored at lower temperatures. HMF generally increased significantly for all nectars during storage. Conversely, the total polyphenol content and the antioxidant activity of the nectars stored in aluminium cans and the larger‐sized carton packaging decreased during storage. Lower anthocyanin loss and colour change were found in the nectars stored in aluminium cans. However, the better packaging material was found to be the large‐sized carton package when HMF was analysed.     

Changes in Volatile Flavor Components of Guava Puree during Processing and Frozen Storage

The changes in volatile flavor components of guava puree during processing (85–88°C, 24 sec) and storage at 0°C, - 10°C and -20°C for up to 4 months was evaluated by Likens-Nickerson distillation and capillary GC-MS. Pasteurized guava puree showed increases in aldehydes and hydrocarbons with decrease in esters when compared with unpasteurized puree. There was only a slight decrease in alcohols and hydrocarbons of pasteurized guava puree stored at - 20°C for 4 mo. Remarkable increases in ethyl alcohol, n-hexanal, decanoic acid, dodecanoic acid and ethyl acetate in pasteurized guava puree were observed when stored at 0°C and - 10°C for 2 and 4 mo, respectively.     

Protective effect of cysteine—HCl on vitamin C in dehydrated pickled/candied pineapples and guava

Dehydrated pickled/candied guava and pineapples pretreated with 0.24 g kg^?1 cysteine hydrochloride (cys-HCl) had increased ascorbic acid retention and reduced colour change during storage. Dehydrated pineapples pretreated with cys-HCl had two to three times the ascorbic acid content of control or metabisulphite-treated products. The rate of ascorbic acid loss for all products stored at room temperature were similar, showing that cys-HCl was only protective towards ascorbic acid during the preparation and dehydration process. Candied dehydrated guava showed less colour change and higher ascorbic acid retention (about 57%) than pickled guava (ascorbic acid retention about 30%). Cys-HCl was quite effective in reducing browning of candied pineapples but not pickled pineapples. Sensory evaluation showed that candied guava pretreated with 0.24 g kg^?1 cys-HCl was generally preferred over the other dehydrated guava products. Cys-HCl-treated candied pineapples had the best flavour compared with all other dehydrated pineapple products. Cys-HCl appeared to favour conversion of glucose to fructose during storage of dehydrated pineapples.     

Optimization of oven drying conditions for lycopene content and lipophilic antioxidant capacity in a by-product of the pink guava puree industry using response surface methodology

Response surface methodology (RSM) was applied to optimize the oven drying conditions for lycopene content (Y₁) and lipophilic antioxidant capacity (Y₂) in decanter, a by-product of the pink guava puree industry. Two-factor central composite design was employed to determine the effects of two independent variables, namely temperature (X₁: 50-80 °C) and drying time (X₂: 4-6 h). Lycopene content and lipophilic antioxidant capacity were measured using high-performance liquid chromatography (HPLC) and the ABTS radicals scavenging assay, respectively. A β-carotene bleaching assay was also applied to measure the antioxidant activity. Response surface plots showed that an increase in temperature and time significantly reduced the response variables. The optimum oven conditions for drying of decanter with minimum lycopene degradation were 43.8 °C for 6.4 h, with a predicted lycopene content of 14 mg/100 g and antioxidant capacity of 21 μmol LE/100 g. To validate the optimized model, the experimental values were compared with the predicted values to check the adequacy of the model. The experimental values were found to be in agreement with those predicted, indicating the suitability of the model for optimizing the oven drying conditions for decanter.     

Influence of pumpkin puree and guar gum on the bioactive,rheological, thermal and sensory properties of ice cream

The effects of pumpkin puree and guar gum on the bioactive, rheological, thermal and sensory properties of ice cream were investigated. The addition of pumpkin puree increased total phenolic content, dietary fibre, and antioxidant activity. Appropriate models described shear thinning and thixotropic behaviours of all mixes. By either adding pumpkin puree or by increasing guar gum concentration, all rheological properties increased except the flow behaviour index. Adding pumpkin puree reduced the freezing point temperature, ice content, frozen water and glass transition temperature but it increased unfreezable water. Increasing guar gum concentration did not alter colour and firmness, whereas the pumpkin puree increased colour, intensity of fruit flavours and firmness.     

Physical-Chemical Characteristics of Partially Clarified Guava Juice and Concentrate

Partially clarified guava juice concentrate was prepared from single strength guava puree (5.5°Brix) by treatment with pectinase (2 hr at 50°C), extraction of juice with a rack-and-cloth press, and vacuum concentration to 23°Brix. The concentrate had the following characteristics: density, 1.10; pH, 3.16; total acids, 4.67%; ash, 1.51%; moisture, 72.4%; ascorbic acid, 867 mg%; viscosity, 4.4 cp; and CIE L* 39.2, CIE a* 10.33, CIE b* 27.11.     

Calcium Oxalate Crystals: The Irritant Factor in Kiwifruit

The cause of irritation in the mouth, when kiwifruit nectars and dried kiwifruit products are ingested, was investigated. Idioblast cells that contain raphide crystals of calcium oxalate were isolated from inner pericarp tissue of the fruit and studied by light and electron microscopy. An experienced panel of 9 judges detected an irritation from sweetened apple puree when isolated raphide crystals were incorporated at the rate of 30 mg oxalate/100g of puree. Sensory and microscopic studies showed evidence that the irritation was caused by sharp calcium oxalate crystals exposed during processing.     

Juice extraction from apples and other fruits and vegetables

Presses are the usual and traditional method of removing juice from fruit and vegetable materials. However, recently diffusion extraction, centrifugation, and specialized ultrafiltration techniques have been explored and have been exploited commercially to a limited extent. Yield efficiency diagrams that relate juice yields to mash feed rates provide a mechanism for comparing presses and other processes such as enzyme treatments or decanter centrifuges for efficiency under a stated set of circumstances. Diffusion extraction is capable of removing 90 to 94% of soluble solids from properly prepared apple slices, but the resulting juice is diluted with extraction water and is high in extracted tannins. Concentration is necessary to obtain juice solids equivalency, and the resulting juice has sour/astringent flavors that must be removed with tannin absorbants to provide acceptable flavor. Currently, decanter centifuges are used commercially and have provided an alternative to presses under certain circumstances. When naturally colored and flavored (unoxidized) juices are desired, the decanter provides a useful alternative to presses because it is easily inert gas blanketed. Utilization of a metallic ultrafilter as a press has been patented but has not achieved commercial utilization. The technical literature describing the application of these juice extraction juices, primarily to apples, is reviewed extensively.     

Behaviour of aroma volatiles during the evaporative concentration of some tropical fruit juices and pulps

The dynamics of aroma separation from some tropical fruit juices and pulps was studied using a thin film evaporator. In the case of mango (Mangifera indica Linn, Alphonso and Totapuri varieties) and guava (Psidium guajava Linn) pulps, 90% of each of the volatile fraction, esters, carbonyls and alcohols, was removed at 30–35% evaporation of the water in a single pass. In the case of pineapple (Ananas sativa Schult F) juice, 90% separation of esters and carbonyls required about 80% and 47% evaporation, respectively. However, the behaviour of alcohols in pineapple juice was found to be similar to that of mango and guava. Mango pulp from Alphonso and Totapuri varieties on 60% evaporation showed a loss in oxygenated terpenes of 80% and 63%, respectively, while guava pulp lost about 58% oxygenated terpenes on 60% concentration. The dynamics of the total aroma volatiles separation from the fruit juices and pulps showed that, in a single pass evaporation, 85–90% volatiles were removed at a juice evaporation degree of 60% water, while the same extent of aroma removal occurred at 32–35% total evaporation by multiple pass.     

Sensory evaluation and physicochemical optimisation of soy-based desserts using response surface methodology

The objective of this study was to develop a dessert that contains soy protein (SP) (1%, 2%, 3%) and guava juice (GJ) (22%, 27%, 32%) using Response Surface Methodology (RSM) as the optimisation technique. Water activity, physical stability, colour, acidity, pH, iron, and carotenoid contents were analysed. Affective tests were performed to determine the degree of liking of colour, creaminess, and acceptability. The results showed that GJ increased the values of redness, hue angle, chromaticity, acidity, and carotenoid content, while SP reduced water activity. Optimisation suggested a dessert containing 32% GJ and 1.17% SP as the best proportion of these components. This sample was considered a source of fibres, ascorbic acid, copper, and iron and garnered scores above the level of ‘slightly liked’ for sensory attributes. Moreover, RSM was shown to be an adequate approach for modelling the physicochemical parameters and the degree of liking of creaminess of desserts.     

WHITE GUAVA FRUIT AND PUREES: TEXTURAL AND RHEOLOGICAL PROPERTIES AND EFFECT OF THE TEMPERATURE

This study focuses on the effect of temperature on the rheological properties of white guava puree. The results of the textural analysis on the whole guava as well as the rheological analysis on the puree made from it showed different behaviors depending on whether the fruit was unripened or ripened. A relationship was observed between the textural properties of the whole guava and the rheological parameters of its puree. The behavior of white guava puree was thixotropic and pseudoplastic, and its rheological properties were dependent of the temperature. Its consistency coefficient decreased and its flow behavior index increased with an increase in temperature. Experimental data were fitted by the power law, and the activation energy of the process was calculated from the Arrhenius equation. Oscillation test data showed that the viscoelasticity for the guava puree was also affected by temperature.

PRACTICAL APPLICATIONS

Knowledge of the rheological properties of foods is useful for quality control, and design and evaluation of process equipment. In this study, it has demonstrated the relationship between textural properties of whole white guava fruit and rheological properties of the purees obtained from these fruits.     

Nutrient composition of extruded cowpea products

Three cultivars of cowpeas (Ife brown, Vita 5 and California black eye) were blended with either rice, corn or both rice and corn and banana puree. The blends were dry extruded on a low cost extruder. The average energy content was 440 Kcal/100 g, protein 20% and the trypsin inhibitor activity was reduced by 63–84%. The stachyose contents varied from 0.52 to 2.44%, raffinose 0.16 to 4.32% and sucrose 0.18 to 1.16 g% respectively. The colour of the products was acceptable and there was no evidence of browning in the products.     

Colour degradation and rheology of green chilli puree during thermal processing

The kinetics of degradation of both green- and total-colour of green chilli puree was studied at selected temperatures (50–90 °C). A fractional conversion concept was applied to determine the kinetic parameters. The degradation of green- and total-colour followed first order reaction kinetics. In the case of green colour the data was based on changes in Hunter – a value while L  ×  a  ×  b was found to adequately represent total colour change. Dependence of the rate constant during heat treatment obeyed the Arrhenius relationship. The activation energy values for green- and total-colour degradation were 23.04 and 25.02 kJ mol^–1, respectively. These results indicated that total colour should be used as the quality indicator during thermal processing of green chilli puree. The pungency of green chilli puree decreased during thermal processing as the capsaicin content was reduced from 559 to 441 μg g^–1 while the Scoville heat unit decreased from 8500 to 7480. The puree behaved as a shear-thinning fluid and the flow activation energy at 100 r.p.m. equalled 19.22 kJ mol^–1.