Date Vinegar: First Isolation of Acetobacter and Formulation of a Starter Culture.

There is a lack of scientific analysis and control over the production of date vinegar in Oman, despite its growing demand in the worldwide market. Traditional production of date vinegar may lead to elevated amounts of ethanol (≥0.5%) and reduced content of acetic acid (<4%) compared to the standard acceptable levels. This study aimed to isolate non-Gluconobacter species from date vinegar produced by spontaneous fermentation and formulate starter cultures for quick and efficient production of date vinegar. In spontaneous fermentation date vinegar samples, the highest concentration of acetic acid was 10.42% on day 50. Acetobacter malorum (5 isolates), A. persici (3 isolates), and A. tropicalis (3 isolates) were identified based on 16S rRNA gene sequences for the first time in date vinegar. For date vinegar prepared with a starter culture of Acetobacter and yeast, the highest concentration of acetic acid was 4.67%. In conclusion, spontaneous fermentation resulted in the production of date vinegar with a high concentration of acetic acid, acceptable concentrations of ethanol and methanol, and the first isolation of three Acetobacter species. The formulated starter culture produced acceptable amounts of acetic acid and the time of fermentation was reduced 10 times (from 40 days to 4 days). This can provide the basis for producing a personalized or commercial product that ensures the production of good-quality date vinegar in an easier, faster, safer, and more efficient way from low-quality and surplus dates.

Thermal and structural characteristics of date-pits as digested by Trichoderma reesei.

The objective of this study was to develop functional date-pits by mold digestion for the potential use in food products. Whole date-pits (WDP) and defatted date-pits (DDP) were digested by mold Trichoderma reesei at 20 °C. T. reesei consumed date-pits as nutrients for their growth, and DDP showed higher growth of molds as compared to the WDP. The mold digested WDP and DDP samples showed an increased water solubility and hygroscopicity as compared to the samples prepared by autoclaved. This indicated that the mold digestion transformed date-pits to hydrophilic characteristics. Thermal analysis indicated a structural change at -3.2 °C for the untreated WDP and it was followed by a glass transition shift (i.e. onset: 138 °C and a specific heat change: 295 J/kg oC), and an endothermic peak at 196 °C with enthalpy of 68 J/g for the solids melting-decomposition. Similar characteristics were also observed for treated samples with the two glass transitions. The total specific heat changes for WDP, autoclaved-WDP, and digested-WDP were observed as 295, 367, and 328 J/kg oC, respectively. The total specific heat changes for DDP, autoclaved-DDP, and digested-DDP were observed as 778, 1329, and 1877 J/kg oC, respectively. This indicated that mold digestion transformed more amorphous fraction in the DDP. The energy absorption intensities of the Fourier Transform Infrared (FTIR) spectra for the selected functional groups decreased by the mold digestion.

Efficiency of Electronic Nose in Detecting the Microbial Spoilage of Fresh Sardines (Sardinella longiceps).

The assessment of microbial spoilage in fresh fish is a major concern for the fish industry. This study aimed to evaluate the efficiency and reliability of an electronic nose (E-nose) to detect microbial spoilage of fresh sardines (Sardinella longiceps) by comparing its measurements with Total Bacterial Count (TBC), Hydrogen Sulfide (H2S) producing bacterial count and Trimethylamine Oxide (TMAO) reducing bacterial count after variable storage conditions. The samples were stored at 0 °C (0, 2, 4, 6, and 8 days) and 25 °C (0, 3, 6, and 9 h), while day 0 was used as a control. The E-nose measurements were analyzed by Principal Component Analysis (PCA), Linear Discriminant Analysis (LDA) and Artificial Neural Network (ANN). Microbial counts increased significantly and simultaneously with the changes in E-nose measurements during storage. The LDA and ANN showed a good classification of E-nose data for different storage times at two storage temperatures (0 °C and 25 °C) compared to PCA. It is expected as PCA is based on linear relationships between the factors, while ANN is based on non-linear relationships. Correlation coefficients between E-nose and TBC, TMAO-reducing bacterial and H2S-producing bacterial counts at 0 °C were 0.919, 0.960 and 0.915, respectively, whereas at 25 °C, the correlation coefficients were 0.859, 0.945 and 0.849, respectively. These positive correlations qualify the E-nose as an efficient and reliable device for detecting microbial spoilage of fish during storage.

Polyphenol and Flavonoid Stability of Wild Blueberry (Sideroxylon mascatense) during Air- and Freeze-Drying and Storage Stability as a Function of Temperature.

But (Sideroxylon mascatense) is an indigenous wild blueberry found in Oman. It has a very short season and is commonly preserved by drying. The aims of this study were to determine the physico-chemical characteristics and stability of phytochemicals (i.e., polyphenols and flavonoids) in the berries during drying (i.e., freeze-drying at -40 °C and air-drying at 60 and 90 °C) and the polyphenol stability of the dried berries as a function of storage temperature (i.e., 90, 70, 60, 40, 20, and -20 °C). The moisture content of fresh berry flesh was 64.5 g/100 g sample (wet basis). The crude protein and fat contents were higher in the seeds than in the flesh. Glucose and fructose were the main sugars and their concentrations were highest in the sample air-dried at 60 °C. The initial total polyphenol content (TPC) and total flavonoid content (TFC) of the flesh were 2.009 mg gallic acid equivalent (GAE)/g dry-solids and 0.199 mg catechin equivalent (CE)/g dry-solids, respectively. The samples air-dried at 90 °C and freeze-dried at -40 °C had higher TPC (i.e., 2.638 mg GAE/g dry-solids) and TFC (i.e., 0.395 mg CE/g dry-solids), respectively. There was a significant difference between the TPC and TFC of fresh and dried wild berries (p < 0.05). The freeze-dried wild berries retained a high TPC compared to the air-dried samples. The polyphenol storage stability of freeze-dried wild berries at different storage temperatures showed two phases: an initial release phase followed by a decay phase. The polyphenol storage stability was modeled using the Peleg model and the kinetic parameters were correlated with the storage temperature.

Possibility of using low-field nuclear magnetic resonance (LF-NMR) and differential scanning calorimetry (DSC) to monitor frying oil degradation.

In this work, chemical degradation of oil was determined as a function of frying time during intermittent deep-fat frying (i.e. 185 °C for 5 h per day for 12 days) and was correlated with the thermal characteristics as measured by Differential Scanning Calorimetry (DSC) and proton mobility by Low-Field Nuclear Magnetic Resonance (LF-NMR). Linear increases of FFAs and PV were observed as a function of frying time. FFAs and PV were strongly correlated with the melting enthalpy. The melting enthalpy of oil decreased exponentially, and the melting temperature remained nearly same until 30 h of frying time followed by a sharp increase. The relaxation times of rigid, semi-rigid and mobile protons (i.e. T 2b , T 21 , and T 22 ) decreased with the increase of frying time. The decrease of T 21 , and T 22 were steeper as compared to the T2b. A strong correlation was observed between conventional chemical parameters (i.e. PV and FFAs), and T 21 and T 22. The populations of the three pools of protons as identified by Inverse Laplace Transformation and Gaussian distribution function showed the interchange of the protons with the chemical changes during frying. It is concluded that chemical free DSC and LF-NMR could be potential methods to monitor frying oil degradation.

Effects of crystallization temperature on the characteristics of sugar crystals in date fruit syrup as measured by differential scanning calorimetry (DSC), polarized microscopy (PLM), and X-ray diffraction (XRD).

Characteristics of sugar crystals are important for developing set-syrup due to their contribution to the desired mouth feel when consumed. Two types of set-syrup (i.e. seeds with and without) were developed by storing the syrup at -20, 4 and 15 °C. The melting temperatures (onset and peak), and enthalpy of set-syrup without seeds (SN) were 30.2 °C, 74.6 °C and 42.2 kJ/kg respectively. In the case of SN, enthalpy decreased with the decrease of crystallization temperature (P < 0.05), while there was insignificant change in the case of set-syrup with seeds (SW) (P > 0.05). Polarized Light Microscopy (PLM) images showed that finer crystals were formed in the cases of set-syrups (i.e. SN and SW) as the storage temperature was decreased. X-ray diffraction (XRD) analysis showed the formation of different polymorphic sugar crystals. Crystallization temperatures at 4 and -20 °C can be used to produce finer crystals with varied polymorphic characteristics.

Antioxidant, antibacterial and ACE-inhibitory activity of four monofloral honeys in relation to their chemical composition.

Different monofloral honeys from Castilla-La Mancha (Spain) have been studied in order to determine their main functional and biological properties. Thyme honey and chestnut honey possess the highest antioxidant capacity, which is due to their high vitamin C (in thyme honey) and total polyphenolic content (in chestnut honey). On the other hand, chestnut honey showed high antimicrobial activity against Staphylococcus aureus and Escherichia coli, whilst others had no activity against S. aureus and showed very small activity against E. coli. Moreover it was found that the antimicrobial activity measured in chestnut honey was partly due to its lysozyme content. In addition the angiotensin I-converting enzyme (ACE) inhibitory activity was measured, and the ACE inhibition is one mechanism by which antihypertensive activity is exerted in vivo. All the types of honey showed some activity but chestnut honey had the highest ACE inhibitory activity.

Development of novel methods to determine crystalline glucose content of honey based on DSC, HPLC, and Viscosity measurements, and their use to examine the setting propensity of honey.

Crystallization must occur in honey in order to produce set or creamed honey; however, the process must occur in a controlled manner in order to obtain an acceptable product. As a consequence, reliable methods are needed to measure the crystal content of honey (ϕ expressed as kg crystal per kg honey), which can also be implemented with relative ease in industrial production facilities. Unfortunately, suitable methods do not currently exist. This article reports on the development of 2 independent offline methods to measure the crystal content in honey based on differential scanning calorimetry and high-performance liquid chromatography. The 2 methods gave highly consistent results on the basis of paired t-test involving 143 experimental points (P > 0.05, r2 = 0.99). The crystal content also correlated with the relative viscosity, defined as the ratio of the viscosity of crystal containing honey to that of the same honey when all crystals are dissolved, giving the following correlation: µr=1-1398.8∅2.318. This correlation can be used to estimate the crystal content of honey in industrial production facilities. The crystal growth rate at a temperature of 14 °C-the normal crystallization temperature used in practice-was linear, and the growth rate also increased with the total glucose content in the honey.

Effect of high hydrostatic pressure on antimicrobial activity and quality of Manuka honey.

The antimicrobial activity of Manuka honey is of major interest to beekeepers and the honey industry. In this study, the effect of high hydrostatic pressure and thermal treatments on antimicrobial activity and quality parameters (principally, diastase number and hydroxymethylfurfural levels (HMF)) of Manuka honey were investigated. The honey was subjected to different pressures (100-800MPa) at 25°C for a range of holding times (15-120min). The antimicrobial activity was found to increase with applied pressure for a given holding time, while the diastase number and HMF levels remained, more or less, unaffected. The percentage inhibition in microbial growth correlated linearly (R(2)=0.94) with methyglyoxal concentration in the honey after treatment over the entire range of pressure, temperature and holding times studied. Maximum percentage inhibition (78.83%) was achieved when honey was subjected to 800MPa compared to the control (57.93%). Thermal treatments at higher temperatures were found to have a detrimental effect on antimicrobial activity based on percentage inhibition as well as methylglyoxal content. Thus, it can be concluded that the levels of methylglyoxal, and therefore the antimicrobial effect of Manuka honey, can be enhanced by using high pressure processing without adversely affecting honey quality.