Abdullah M. Alhamdan

Water sorption isotherms of date pastes as influenced by date cultivar and storage temperature

Abstract 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.

Residence time distribution of food and simulated particles in a holding tube

Abstract Residence time distribution (RTD) was determined for food and simulated particles flowing in a holding tube, as affected by particle shape (cube, cylinder, sphere), particle concentration (10, 20, and 30% w/v), particle type (potato, carrot, turkey, green peas, and polystyrene), fluid viscosity (0.0% CMC, 0.5% CMC, 1.0% CMC), bulk flow rate (5.81, 7.28, and 8.71 × 10 −4 m 3 /s) and SSHE shaft speed (30, 60, and 90 rpm). Residence times of tracer particles were recorded by a video camera equipped with a timer. Cylindrical particles remained in the holding tube longer than cubic particles. Increasing particle concentration and bulk flow rate tended to decrease mean normalized particle residence time (MNPRT). Increasing fluid viscosity decreased MNPRT significantly, apparently due to the strong lift action of the fluid on the particles. Although turkey particles were denser than other food particles, they had smaller residence times than the carrot and potato particles. The MNPRT of green peas was found to be significantly higher than that of polystyrene spheres. Swept-surface heat exchanger shaft speed did not influence MNPRT in the holding tube. The residence time distribution curves were narrowed by decreasing particle concentration and increasing bulk flow rate, and by using high viscosity fluids and cubic particles. The longest particle residence time was 5.3 times the average bulk residence time. The fastest particle did not exceed 1.8 times the average bulk velocity. This finding is within the conservative value of 2.0 considered safe in sizing holding tubes in aseptic processing systems.

NATURAL CONVECTION HEAT TRANSFER BETWEEN WATER AND AN IRREGULAR-SHAPED PARTICLE

ABSTRACT Natural convection heat transfer was investigated between water and a mushroom-shaped particle, under transient conditions, with various initial temperature differences. Convective heat transfer coefficients (h) were observed to decrease over time due to equilibration, resulting in reduced driving force. In all cases, the average value of h was significantly higher for heating than for cooling. In most cases, h increased significantly with increasing initial temperature difference. When results at the same initial temperature difference were compared, h was higher for the higher temperature ranges. Correlations were developed between Nusselt, Rayleigh, and Fourier numbers.

RHEOLOGICAL PROPERTIES OF A NEWLY NUTRITIOUS DAIRY DRINK FROM MILK AND DATE EXTRACT CONCENTRATE (DIBBS)

Rheological properties of date extract concentrate (dibbs), milk, and milk-dibbs drink of different dibbs concentration were experimentally determined. The dibbs was extracted from three date cultivars (Khlass, Sukkari, and Nubot Seif), and then added to milk in a specified amounts ranging from (2.5 to 15 mL dibbs/100 mL milk) to form the sweetened and nutritious milk-dibbs drinks. It was found that milk, dibbs, and milk-dibbs drinks exhibited pseudoplastic behavior following a power law model at the temperature range 5 to 65°C. The flow behavior indices ranged between 0.705 to 0.888 for dibbs and milk-dibbs drinks based on date cultivar, temperature, and concentration. For the dibbs and milk-dibbs drinks, the consistency index was found to decrease with the increase of temperature, and increase with the amount of dibbs added. Results showed a significant influence of date cultivars on the rheological properties of dibbs and milk-dibbs drink. Utilizing the Arrhenius model, the activation energies ranged from 5×103 kJ kg−1 mol−1 to 21× 103kJ kg−1 mol−1 at shear rate 100 s−1.

Freezing of fresh Barhi dates for quality preservation during frozen storage

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.

Comparative Efficacy of CO2 and Ozone Gases Against Ephestia cautella (Lepidoptera: Pyralidae) Larvae Under Different Temperature Regimes

Comparative efficacy of three different modified atmospheres: 100% CO2, 75% CO2 + 25% N2, and 22 ppm ozone were examined against larval mortality of the almond moth, Ephestia cautella (Walker) (Lepidoptera: Pyralidae) at temperature regimes of 25°C and 35 ± 2°C and 60 ± 5% relative humidity, and 9:15 dark and light. Wandering young larval instars, which are fast growing, large enough in size and considered as more tolerant to modified atmosphere, were collected directly from the rearing culture, placed inside pitted date fruits of vars.: “Khudri,” “Ruziz,” and “Saqie,” were treated with aforementioned gases for 24, 48, and 72 h. The immediate and delayed larval mortality was recorded after each exposure timing. Ozone possessed the strongest fumigant toxicity causing 100% mortality with all varieties, at 25 and 35°C after 24 h exposure and was more effective than 75% CO2 that caused 83 and 100% immediate mortality with variety ruziz at 25 and 35°C, respectively. Extending the treatments exposure time to 72 h, 100% mortality was recorded by exposing larvae to any of the studied gases at 25 and 35°C. These results suggest that gases and temperature used in this study can be effectively used to control E. cautella in dates and stored grains.

Non-destructive method to predict Barhi dates quality at different stages of maturity utilising near-infrared (NIR) spectroscopy

ABSTRACT Barhi dates cultivar (Phoenix dactylifera L.) at Khalal stage of maturity was characterised by its sweetness, crunchiness, and bright yellow colour. Non-destructive and quick tools are necessary to evaluate fruit quality during post-harvest operations. Near-infrared (NIR) spectroscopy is an effective method to detect quality parameters for several fruits. In this study, NIR was utilised to correlate quality parameters (total soluble solids, moisture content, and b* colour) at five stages of maturity (from Khalal (green, to yellow), and Rutab (brown) with spectrum analysis. Barhi quality parameters were found to correlate well using NIR with a high coefficient of determination (R2) 0.97 for TSS; 0.94 for MC; and fair of 0.64 for b* colour. It can be concluded that NIR is an effective non-destructive tool to predict fruit quality of Barhi at different stages of maturity during various %post-harvest operations.