Benu Adhikari

STICKINESS IN FOODS: A REVIEW OF MECHANISMS AND TEST METHODS

Problems associated with the stickiness of food in processing and storage practices along with its causative factors are outlined. Fundamental mechanisms that explain why and how food products become sticky are discussed. Methods currently in use for characterizing and overcoming stickiness problems in food processing and storage operations are described. The use of glass transition temperature-based model, which provides a rational basis for understanding and characterizing the stickiness of many food products, is highlighted.

Glass Transition Behavior of Spray Dried Orange Juice Powder Measured by Differential Scanning Calorimetry (DSC) and Thermal Mechanical Compression Test (TMCT)

Spray drying behavior of orange juice concentrate with various levels of maltodextrin (DE 6) was studied. Five combinations of orange juice concentrate and maltodextrin (25:75, 30:70, 35:65, 40:60, and 50:50) were spray dried at 160 and 65°C inlet and outlet temperatures, respectively. The product recovered with 50% maltodextrin concentration was sticky and only 20% powder was recovered. The recovery of orange juice powder increased as the amount of maltodextrin in powders increased. The particle size and bulk density remained almost the same in all except in 50% maltodextrin powder which was slightly larger and more dense. The moisture content of spray dried powders was high and desiccated before measuring glass transition temperature. The anhydrous spray dried powders showed increased Tg values with increasing maltodextrin concentration, from 66°C in 50% maltodextrin to 97°C in 75% maltodextrin containing powders. The glass rubber transition (Tg-r) values of all the products measured using novel Thermal Mechanical Compression Test (TMCT) were higher than Tg values measured by DSC; the difference in values increased with increase in maltodextrin concentration.

Surface Stickiness of Drops of Carbohydrate and Organic Acid Solutions During Convective Drying: Experiments and Modeling

Abstract Drying kinetics of low molecular weight sugars such as fructose, glucose, sucrose and organic acid such as citric acid and high molecular weight carbohydrate such as maltodextrin (DE 6) were determined experimentally using single drop drying experiments as well as predicted numerically by solving the mass and heat transfer equations. The predicted moisture and temperature histories agreed with the experimental ones within 6% average relative (absolute) error and average difference of ± 1°C, respectively. The stickiness histories of these drops were determined experimentally and predicted numerically based on the glass transition temperature (T g ) of surface layer. The model predicted the experimental observations with good accuracy. A nonsticky regime for these materials during spray drying is proposed by simulating a drop, initially 120 µm in diameter, in a spray drying environment.

Characterization of the Surface Stickiness of Fructose–Maltodextrin Solutions During Drying

Abstract A probe tack test has been used for the in situ characterization of the surface stickiness of hemispherical drops with an initial radius of 3.5 mm while drying. Surface stickiness of drops of fructose and maltodextrin solutions dried at 63°C and 95°C was determined. The effect of addition of maltodextrin on fructose solution was studied with fructose/maltodextrin solid mass ratios of 4:1, 1:1, and 1:4. Pure fructose solutions remained completely sticky and failed cohesively even when their moisture approached zero. Shortly after the start of drying, the surface of the maltodextrin drops formed a skin, which rapidly grew in thickness. Subsequently the drop surface became completely nonsticky probably due to transformation of outer layers into a glassy material. Addition of maltodextrin significantly altered the surface stickiness of drops of fructose solutions, demonstrating its use as an effective drying aid.

Experimental studies and kinetics of single drop drying and their relevance in drying of sugar‐rich foods: A review

Abstract Levitation and free‐flight techniques applied to investigate the drying kinetics and morphology of single drops containing dissolved solids and suspensions are reviewed. A review of works related to receding interface model proposed to quantify the drying kinetics of single drops along with techniques to measure the kinetic parameters such as moisture diffusivity, thermal conductivity and specific heat capacity is presented. Problems associated with spray drying of sugar‐rich compounds are briefly discussed and possible links of stickiness and flavor retention with glass transition temperature (Tg), temperature history, drying rate and morphological changes including skin formation, as monitored through single drop experiments, are explored.

In situ characterization of stickiness of sugar-rich foods using a linear actuator driven stickiness testing device

A stickiness testing device based on the probe tack test has been designed and tested. It was used to perform in situ characterization of drying hemispherical drops with an initial radius 3.5 mm. Tests were carried out in two drying temperatures, 63 and 95 degreesC. Moisture and temperature histories of the drying drops of fructose, honey, sucrose, maltodextrin and sucrose-maltodextrin mixtures were determined. The rates of moisture evaporation of the fructose solution was the fastest while those of the maltodextrin solution was the lowest. A profile reversal was observed when the temperature profiles of these materials were compared. Different modes of failure were observed during the stickiness tests. Pure fructose and honey solutions remained completely sticky and failed cohesively until the end of drying. Pure sucrose solution remained sticky and failed cohesively until complete crystallization occurred. The surface of the maltodextrin drops formed a skin shortly after the start of drying. It exhibited adhesive failure and reached a state of non-adhesion. Addition of maltodextrin significantly altered the stickiness of sucrose solution

Application of a simplified method based on regular regime approach to determine the effective moisture diffusivity of mixture of low molecular weight sugars and maltodextrin during desorption

The binary diffusivities of water in low molecular weight sugars; fructose, sucrose and a high molecular weight carbohydrate; maltodextrin (DE 11) and the effective diffusivities of water in mixtures of these sugars (sucrose, glucose, fructose) and maltodextrin (DE 11) were determined using a simplified procedure based on the Regular Regime Approach. The effective diffusivity of these mixtures exhibited both the concentration and molecular weight dependence. Surface stickiness was observed in all samples during desorption, with fructose exhibiting the highest and maltodextrin the lowest.

Spray Drying of Skim Milk Mixed with Milk Permeate: Effect on Drying Behavior, Physicochemical Properties, and Storage Stability of Powder

The possibility of using milk permeate (MP) to lower the protein level of skim milk powder (SMP) in producing powders of 34% and lower protein is explored. Skim milk suspensions with various levels of MP were prepared by mixing SMP and MP powder (MPP) at the ratios of 1:0, 7:3, 3:7, and 0:1: from 34 to 5.3% protein. The suspensions were dried in a spray dryer with inlet and outlet temperatures of 180 and 80°C, respectively. Increasing permeate concentration in the mixture showed a greater tendency to stickiness manifested by lowered the cyclone recovery of the powder as more powder stuck on the wall of the dryer. Increasing permeate concentration in the resultant powder did not significantly affect the bulk density but led to a reduction in the particle size and also made the powder slight green and yellowish in color. It also found to lower the glass transition temperature (Tg ) of the skim milk powder (SMP) and induce crystallization of lactose at lower water activity (aw ≥ 0.328 for SMP:MPP of 3:7 and 0:1 compared to aw ≥ 0.0.432 for SMP:MPP of 1:0 and 3:7). Addition of MP in SMP lowered the Tg values of the resulting powders. The permeate fraction in spray-dried SMP/MPP mixtures found to lower the critical aw and moisture content, suggesting the SMP mixed with MPP is more likely to become sticky than SMP alone (at 34% protein) when stored at a similar water activity and moisture content.

Effect of plasticizers on the moisture migration behavior of low-amylose starch films during drying

We report the synergistic and competitive interactions between multiple plasticizers in plasticized low-amylose starch that result in either enhanced or reduced water migration fluxes and effective moisture diffusivities. The starch was plasticized using glycerol and xylitol either individually or in 1:1 combination. The water migration fluxes and moisture diffusivities were higher in xylitol plasticized films compared to the glycerol plasticized ones. For low plasticizer concentrations, the presence of both the plasticizers competitively reduced the effective moisture diffusivities and moisture migration fluxes due to antiplasticization. However, at higher plasticizer contents (at and above 15 wt%), the presence of multiple plasticizers enhanced the moisture migration fluxes and effective moisture diffusivities due to synergistic plasticization. The moisture migration fluxes and effective moisture diffusivities exhibited both moisture and plasticizer concentration dependence and the former was found to be stronger than the latter. These findings can be used for designing and controlling the vapor barrier properties of starch-based bioplastics during drying and formulation phase.

Artificial neural networks: a new tool for prediction of pressure drop of non-Newtonian fluid foods through tubes

Pressure gradients and the corresponding mass flow rates of five different non-Newtonian fluid foods: 1% solutions of sodium alginate and CMC, 1.5% CMC solution, two different tomato ketchups, oyster sauce, in four different diameter stainless steel tubes ranging from 7.51 to 16.34 mm i.d. were recorded using a continuous recording type tube flow viscometer capable of operating in both transient and continuous flow modes. The fluids were pseudoplastic in nature and followed the power law model. The flow was confined to the laminar flow regime and appreciable slippage occurred in all cases. Commercially available artificial neural networks based on back-propagation and generalized regression algorithm were applied to predict the pressure gradients in tube flow providing mass flow rate, consistency coefficients and flow behavior indices obtained from a low shear rate rotational viscometer, mass density and tube diameters as inputs. The net predicted values closely followed the experimental ones with an average absolute error below 5.44%.