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Physical properties of Sukkari date powder (SDP) at different particle sizes, namely, moisture content, water activity, tapped and bulk densities, compressibility index, Hausner ratio, water absorption, and solubility indices, swelling capacity, and color parameters were experimentally determined. The SDP moisture sorption experiments were conducted using a dynamic vapor sorption instrument in the relative humidity range 10%–90% at 20, 40, and 60°C. Among the ten tested sorption models, the GAB and modified GAB models best fitted SDP sorption data. The monolayer moisture content decreased with increasing temperature. The differential enthalpy and entropy, and net integral enthalpy and entropy decreased consistently with increasing moisture content. The linear relationship between differential enthalpy and entropy confirmed the applicability of the compensation theory. The estimated values of the isokinetic and harmonic temperatures and the Gibbs free energy change revealed that the sorption process is non-spontaneous and enthalpy driven.

Fresh harvested dates are perishable and there is a need for extending their shelf life while preserving their fresh like quality characteristics. This study evaluates three different freezing methods, namely cryogenic freezing (CF) using liquid nitrogen; individual quick freezing (IQF) and conventional slow freezing (CSF) in preserving the quality and stability of dates during frozen storage. Fresh dates were frozen utilizing the three methods. The produced frozen dates were frozen stored for nine months. The color values, textural parameters, and nutrition qualities were measured for fresh dates before freezing and for the frozen dates every three months during the frozen storage. The frozen dates’ color values were affected by the freezing method and the frozen storage period. There are substantial differences in the quality of the frozen fruits in favor of cryogenic freezing followed by individual quick freezing compared to the conventional slow freezing. The results revealed large disparity among the times of freezing of the three methods. The freezing time accounted to 10 min for CF, and around 80 min for IQF, and 1800 min for CSF method. Keywords: Freezing methods, Frozen storage, Barhi dates, Quality preservation, Color values

Fresh date fruits, especially Barhi cultivar, are favored and widely consumed at the Khalal maturity stage (first color edible stage). These fruits are seasonal and perishable and there is a need for extending their shelf life. This study evaluates two different freezing methods, namely cryogenic freezing using liquid nitrogen and conventional deep freezing on preserving the quality and stability of date fruits (cv. Barhi ) at Khalal maturity stage. Fresh date fruits (cv. Barhi ) at Khalal stage were frozen utilizing the two methods. The produced frozen dates were stored under frozen storage conditions for nine months (at −20 °C and −40 °C for the conventional and cryogenic freezing, respectively). Color values, textural properties (hardness, elasticity, chewiness and resilience), and nutrition attributes (enzymes and sugars) for fresh dates before freezing and for the frozen dates were measured every three months during the frozen storage. Color values of the frozen dates were affected by the freezing method and the frozen storage period. There are substantial differences in the quality of the frozen fruits in favor of cryogenic freezing compared to the conventional slow freezing. The results revealed a large disparity between the times of freezing of the two methods. The freezing time accounted to 10 min in the cryogenic freezing method, whereas it was 1800 min for the conventional slow freezing system.

Fresh date fruits (Barhi cultivar) at Khalal stage of maturity were frozen by two different methods; individual quick freezing (IQF), and conventional slow freezing (CSF). The frozen dates were stored for 9 months at -20°C and -40°C, through conventional and individual quick freezing methods, respectively. Texture profile analysis parameters (hardness, elasticity, chewiness and resilience), color, and nutrition (enzymes and sugars) properties for fresh and frozen dates were measured after every three months of frozen storage. IQF technique showed better result in quality maintaining of fresh date fruits than CSF. Color and textural parameters of the frozen dates were affected by the freezing method and the frozen storage period. IQF method is superior in preserving the fresh Barhi fruits color values, textural parameters and nutritional aspects compared

The effects of modified atmosphere packaging (MAP) on various physicochemical quality attributes of fresh Barhi dates at the Khalal (yellow) stage were studied. Polypropylene (PP) and polyethylene (PE) plastic with varied perforation sizes (0, 50, 100 and 150 µm) were evaluated for storage of date fruits at temperatures of 1, 5, 15 and 25 °C up to 45 days. MAP showed significant effects on fruit quality. PP date packages perforated with 150-µm perforations and stored at 5 °C had the lowest acidity and microbial load. Dates packed in PE exhibited higher pectin methylesterase (PME) and polyphenol oxidase (PPO) activities than dates packed in PP. Dates stored in nonperforated packages had the highest PME, PPO and invertase activities. The maximum fructose and glucose contents were observed in PP-packaged dates stored at 15 °C. Analysis of the interactions of several MAP variables revealed temperature as the major variable controlling the quality of dates. The findings showed that MAP can be effectively employed to preserve the quality and improve the shelf life of Barhi dates using PP with 150-µm perforations as the packaging material during storage for 2 weeks at 5 °C.

Convective hot air drying was used to dry date fruits at different air temperatures and velocities. The kinetics of drying was evaluated by 10 common models. The fruit color and texture were examined before and after drying. Drying time increased as both drying temperature and air velocity decreased. Best fits to the experimental data were provided by the Midilli and Kucuk model, followed by the logarithmic, two-term exponential, and Henderson–Pabis models. Drying affected the fruit color and texture. To minimize such changes, the range of drying temperature and air velocity should be 60–70°C and 2 m/s, respectively.

The conformity of Saudi dates cultivars to date standards has not been studied extensively. In this study, microbial loads and physicochemical characteristics of four Saudi date cultivars (Sukkary, Khalas, Sugai and Anbara) were determined. Anbara cultivar had significantly higher mould and yeast counts than recommended under Saudi technical regulation and standards for packaged whole dates. Moisture content and insect damage for all studied cultivars fell within Codex standards. Single fruit weight for pitted and unpitted dates was higher than recommended under international standards. Date cultivar had a significant effect on fruit color thus fruit color should be included in Saudi technical regulation and standards for date grading.

Modified atmosphere packaging (MAP) was evaluated for total phenolic contents (TPC), antioxidant, tannin, color, and sensory properties of fresh Barhi dates. Polypropylene (PP) and polyethylene (PE) with different perforations (0 [H0], 50 µm [H3], 100 µm [H6], and 150 µm [H9]) were evaluated for storing fresh Barhi dates for up to 45 days at 1 to 25°C temperature. MAP significantly (p ≤.05) affected the properties investigated as compared to control. PE dates have higher (p ≤.05) TPC than PP dates, whereas other properties remained largely unaffected by packaging material. TPC and antioxidant activity were higher (p ≤.05) in H0 treated dates. H9 perforated packaged dates exhibited higher (p ≤.05) tannin contents, better sensory and color attributes. Barhi dates exhibited fresh-like quality and better antioxidant properties at low storage temperature (5°C) for up to 2 weeks’ storage and similar was verified by principal component analysis using HJ plots where storage temperature was observed as major factor. Practical applications: Modified atmosphere packaging or MAP is an emerging technique for preserving fresh fruits and vegetables and it is being studied extensively for different fresh commodities in order to preserve their fresh like characteristics. There is a need to study MAP effects on storing new and economically important fruits such as Barhi dates which have shorter life in early stages of maturity but cherished when freshly harvested due to various health benefits and characteristic taste and quality. MAP was effectively tested and applied for preserving Barhi dates and MAP variables were evaluated in order to find the best packaging conditions which may ensure maximum consumer benefits and date quality.

Summary. Dried sheets (Teen-Edin) from prickly pear (Taifi cultivar) fruits were made and the composition of the pulp and the optimum formulation sheet was analysed. The optimum formulation was obtained by adding to fruit pulp (100%), 10% sucrose, 1.1% citric acid, 0.15% sodium metabisulphite, and 0.5% olive oil (w/w). Sodium metabisulphite improved the colour and citric acid produced a similar acid taste to the traditional apricot sheets. The sheets were highly acceptable to a small panel and have potential for manufacture as a possible alternative to apricot sheets (Kamar-Eddin). The technique could also be used for preservation in many other arid parts of the world where prickly pears grow.

The viscoelastic nature of eight date cultivars at their khalal (balah) and rutab stages of maturity were studied by estimating their relaxation parameters from experimental stress relaxation data. Three popular stress relaxation models, namely the generalized Maxwell, Nussinovitch, and Peleg were fitted to experimental data. All three models were valid for quantifying the relaxation behavior of dates; however the generalized Maxwell was the best in predicting experimental data.

Thin-layer drying rates of two date cultivars, namely, Sukkari and Sakie were experimentally determined at three drying temperatures 70, 80, and 90C. Three drying models were evaluated for the thin-layer date data. These were the exponential model, Page equation, and the approximation of diffusion model. The Page equation fitted the data best. Two empirical expressions of Page equation for predicting moisture ratio as a function of drying time and drying temperature for the two date cultivars are presented.

The water sorption isotherms of pastes of three date cultivars – Ruziz, Khudari, and Khlass – were determined using the static method of saturated salt solutions at three storage temperatures: 5°C, 25°C and 40°C. The effect of temperature on sorption behavior was more pronounced than the effect of date cultivar. Equilibrium moisture content decreased with increasing temperature at water activities below 0.45–0.55. However, above 0.45–0.55, equilibrium moisture content increased with increase in temperature, mainly due to the additional dissolution of sugars at higher temperatures. The experimental data fitted well with GAB, Iglesias and Chirife, and Halsey equations, suitable for high sugar foods.

Flow properties of water extract of Roselle calyces were determined using a concentric cylinders rotational viscometer for extract concentration range of 5–65% TS, temperature range of 20–60 °C, and shear rate range of 2·5–979 s−1. Measured shear stress was within the range 0·5 to 49·7 Pa, corresponding to an apparent viscosity range of 0·0015–1·55 Pa s. Within the tested ranges of concentration, temperature, and shear rate, the extract exhibited a pseudoplastic behaviour, and was adequately described by the simple power law model. The flow behaviour index was consistently below unity (0·76–0·97), with the consistency index varying between 0.007 and 1.6 Pa sn. Activation energy of flow varied from 18·74 to 42·80 (kJ/kmol) for the extract concentration range of 5–65% TS, at a shear rate of 100 s−1. The experimental results were fitted by mathematical models to allow prediction of apparent viscosity as a function of concentration, temperature, and shear rate.

Hibiscus sabdariffa (Roselle) powder was produced by pilot scale spray drying using single strength and vacuum concentrated water extract of its calyces. Powders were analyzed for moisture, protein, vitamin C, total soluble solids (TSS), pH, particle size, bulk density, solubility, dispersibility, hygroscopicity, and microbiological status. The lowest inlet air temperature (198.5 degrees C) resulted in the product with best protein content (12.43%), retention of vitamin C (82.76 mg/100g), and solubility (dissolving in 97 sec); as well as the highest moisture content (3.78%) in the product. The powder showed a noticeable tendency to stick to internal surfaces of the drying chamber particularly with concentrated solutions at higher temperatures.

Heat transfer rates were measured for steam-heated, rotating cans containing potato spheres in water. Can rotational speed (9.3–101 rpm), sphere size (22.2–35.0 mm), and potato volume fraction (0.107–0.506) were varied in 14 triplicated experiments. Overall heat transfer coefficients were correlated within ±25% with physical properties and operating variables by an equation derived by dimensional analysis. Film coefficients (hp) for heat transfer from the water to potatoes in the can were determined by thermocouple measurement of potato surface temperatures; values were found to be finite and nearly invariant, averaging hp= 160 ± 30 W/m2K. The lack of variation of hp suggested that for the experimental conditions tested, there was little relative motion between liquid and particles.