The rate of non-enzymatic browning reaction in model freeze–dried food system in the glassy state

Vacuum Dehydration: An Excellent Method to Promote the Formation of Amadori Compounds (ACs, N-(1-Deoxy-d-fructos-1-yl)-amino Acid) in Aqueous Models and Tomato Sauce

Amadori compounds (ACs; N-(1-deoxy-d-fructos-1-yl)-amino acid) are superior flavor precursors and potential functional ingredients in food processing. In this study, vacuum dehydration as an excellent and universal method for the formation of ACs in both simulation systems and food processing was revealed. In total, 12 amino acids referring to all six categories were selected to conduct simulated reactions with glucose in aqueous models. At 90 °C, yields of 11 ACs were significantly increased by vacuum dehydration, reaching 4-198 times compared to a heat sealing reaction in aqueous systems, and formation of 5-hydroxymethyl-2-furaldehyde (5-HMF) and browning were slower than that by a dry powder reaction. In particular, the yields of Fru-Arg, Fru-His, and Fru-Glu reached 87.03, 90.73, and 89.88 mol %, respectively. The order of promotion effect was acid ACs > basic ACs > unique ACs > polar neutral ACs > aliphatic ACs > aromatic ACs. The excellent effect was mainly attributed to the control of water activity (Aw) and pH, which enabled the models to reach the optimal reaction state quickly by adjusting the vacuum degree at mild temperatures. The method was also applied to AC enrichment in tomato sauce processing; the AC content could rise to 30.72 mg/g, which was more than 17 times than those in samples without vacuum dehydration and two commercial tomato sauces.

Hygroscopic properties and glass transition of dehydrated mango, apple and banana

An undesirable crispiness loss occurs when some dry fruits reach a critical moisture content (X_c ) and their glass transition temperature (T_g ) matches the storage temperature. Models for sorption isotherms and onset T_g values for dry mango, apple, and banana were used to estimate X_c values at 25 and 32 °C. All models yielded R² > 0.97 but information theory criteria strongly supported GAB in all but one case (40 °C, mango). The Gordon-Taylor T_g model (GT) yielded high R² values for apple and banana but resulted in R² = 0.834 for mango. As moisture approached zero, mango T_g estimates displayed a downward concavity contrasting with a rapidly increasing trend for apple and banana. The Khalloufi-Maslouhi-Ratti (KMR) model for T_g as a function of a_w showed a linear behavior. Although the KMR model fitted data with R² > 0.996, it requires more parameters and when a_w approached 0, estimated T_g values increased at a slower rate than for the GT model. In the case of banana and mango, both models predicted approximately the same X_c at 25 °C but not at 32 °C. Finally, all X_c values estimated based on T_g were lower than the monolayer values obtained with the GAB (apple and banana) and BET (mango) models. These results indicate that the glass transition induced by moisture uptake dominates the quality degradation of these dry fruits.

Preparation of activated flavor precursor DFG, N-(1-deoxy-1-fructosylglycine) by combination of vacuum evaporation and closed system heating steps

Amadori rearrangement products are potent "activated flavor precursors". This study describes a stepwise optimization of DFG (1-deoxy-1-fructosylglycine) formation from glycine and glucose, varying temperature, water activity a_w, concentration, and ratio/state of precursor mix. In the solid state reaction at 50 °C for 16 h, yield of DFG increased with decreasing water activity with a peak at a_w = 0.22-0.33. In water the conversion was slower and negatively correlated with water activity in the range a_w = 0.8-1. An industrially applicable 2-step vacuum drying and heating process was explored, which first concentrates precursor solution to a_w = 0.5-0.6 and then continues the heating in a closed vessel for an additional 2-4 h. Over 40 mol% conversion from glucose to DFG was obtained on a multi-gram scale. Fine tuning of conditions will be needed for other amino acid/carbohydrate combinations and may offer new perspectives for tailored product flavor generation under moderate heating.

Stabilizing Effect of Four Types of Disaccharide on the Enzymatic Activity of Freeze-dried Lactate Dehydrogenase: Step by Step Evaluation from Freezing to Storage

PURPOSE

In order to understand the stabilizing effects of disaccharides on freeze-dried proteins, the enzymatic activity of lactate dehydrogenase (LDH) formulations containing four types of disaccharide (trehalose, sucrose, maltose, and lactose) at two relative humidity (RH) levels (about 0 and 32.8%) was investigated after three processes: freeze-thawing, freeze-drying, and storage at three temperatures (20, 40, and 60 degrees C) above and/or below the glass transition temperature (T(g)).

MATERIALS AND METHODS

The enzymatic activity was determined from the absorbance at 340 nm, and T(g) of the samples was investigated by differential scanning calorimetry.

RESULTS

At each RH condition, T(g) values of sucrose formulations were lower than those of other formulations. Although effects of the disaccharides on the process stability of LDH were comparable, storage stability was dependent on the type of disaccharide. All the formulations were destabilized significantly during storage at temperature above T(g). During storage at temperature below T(g), the LDH activity decreased with increases in the storage temperature and moisture. Maltose and lactose formulations showed significant destabilization with the change of color to browning.

CONCLUSIONS

Taking the storage stability of freeze-dried proteins under the various conditions (temperature and RH) into consideration, trehalose is better suited as the stabilizer than other disaccharides.