with the collaboration of Iranian Food Science and Technology Association (IFSTA)

Document Type : Short Article

Authors

Ferdowsi University of Mashhad

Abstract

Introduction: Malt extract is one of the malt products obtainedfrom concentrations of water soluble extract of grains such as barley and is a proper alternative to white sugar. It has a high diastasis properties andcontainshigh amount of different vitamins specially the group of vitamin B as well as high amount of fermentable sugars. Therefore, malt extract has high nutritional value and is recommended by nutritionist for children and people who are having growth problems. In addition, it has a high potential to be used as sweetening agent in different food products such as cookies, biscuits, ice cream, chocolates etc. Knowledge on the thermo-physical properties of malt extract such as density, specific heat, thermal conductivity as well as thermal diffusivity is highly necessary for the designing of processing equipments, formulation of derived products, heating and chilling processes, and other unit operations such as pasteurization, concentration, dehydration as well as final safety and quality of formulated products. Since, no research work has been reported on thermo-physical properties of malt extract, the aim of this study was to determine different thermal properties of malt extract as well as investigation of the effect of temperature and soluble solid contents (SSC) of the studied properties.

Materials and methods: Barley malt was purchased from local market. 150 gr of malt was first grounded and added to 600ml water at 46°C and stored for 30 minutes. Then, its temperature was increased using a heater to reach 70°C. 300 ml water was then added to the mixture and stored at 70°C for 60 minutes. Then, the mixture was cooled at room temperature and filtered to gain a sweet solution. The obtained solution was concentrated to 60, 70 and 80 degree of Brix for further experiments.
Specific heat and thermal conductivity of samples were determined using a differential scanning calorimeter (DSC). DSC is a powerful tool which is able to spontaneously measure different thermal propertiesof samples such as specific heat, thermal conductivity, glass transition temperature, melting point, crystallization point etc. as a function of time and temperature at the desired temperature levels. Density of samples was also measured using a 50ccvolumetric pycnometer. 25 grams of samples were first solved in hot water and then were placed in an isothermal bath to measure the density. Thermal diffusivity of samples was determined using the following equation:
∝=k/〖pC〗_p

Results and discussion: The obtained results on specific heat measurement showed that decreasing SSC from 80 to 60% and increasing the temperature from 25 to 90°C would increase cp from 2.074 to 3.063 kJ/kg°C in a linear manner. Following equations were obtained to predict specific heat as a function of temperature:
C_p=2.756+0.004T R^2=0.893 ، X_s=60
C_p =2.245 +0.005T 〖 R〗^2=0.868، X_s=70
C_p=2.066 +0.001T R^2=0.75، X_s =80

Thermal conductivity measurements were also showed that decreasing SSC from 80 to 60% and increasing temperature from 25 to 90°C would increase the K values from 0.1196 to 0.347 W/m°C in a linear manner. Increasing temperature would increase molecular movements and therefore it elevates the heat transfer velocity and K increases. Following equations were obtained to predict thermal conductivity as a function of temperature:
K=0.152 +0.003T R^2=0.761، X_s=60
K =0.097+0.002T R^2=0.851، X_s=70
K=0.114+0.001T R^2=0.706،X_s =80

In order to develop a model to predict thermal conductivity of malt extract based on its soluble solid content and temperature, multiple regressions was used. The obtained model was a two-parameter linear model with R2 of 0.858. The results showed that 1% increase in soluble solid content percentage would cause an increase of 6% in K, while 1% increase in temperature would cause only 49% increase in thermal conductivity value.
Density measurements were also showed that increasing density from 60 to 80% and temperature from 25 to 90°C would increase density of malt extract. Following equations were obtained to predict density as a function of temperature:
P=1328.699-0.402T R^2=0.999، X_s=60
P=1375.451-0.290T R^2=0.999، X_s=70
P=1426.201-0.286T R^2=0.998،X_s =80

Thermal diffusivity of samples was also determined using indirect method for soluble solid content of 60 to 80 and in the temperature range of 25 to 90°C. It was found that thermal diffusivity would increase linearly by decreasing soluble solid content and increasing temperature. Following equations were obtained to predict thermal diffusivity as a function of temperature:
∝=5.176〖×10〗^(-8)+0.049×〖10〗^(-8) T R^2=0.783، X_s=60
∝=2.993×〖10〗^(-8)+0.050×〖10〗^(-8) T R^2=0.929، X_s=70
∝=3.125×〖10〗^(-8)+0.036×〖10〗^(-8) T R^2=0.94،X_s =80

The results of the present work were in agreement with the results reported by other researchers confirming that both SSC and temperature have significant effect on thermo-physical properties of malt extract.

Keywords

Beitane I,Straumite E.2014. Effect of hull-Less barley flakes and malt extract onyoghurt quality Biosystems Science and Engineering Vol:8 No:3.
Cabral RAF, Orrego-Alzate CE, Gabas AL, Telis-Romero J.2007. Rheological and thermophysical properties of blackberry juice. Food Science and Technology (Campinas);27(3):589-95.
Coimbra JS, Gabas AL, Minim LA, Garcia Rojas EE, Telis V, Telis-Romero J.2006. Density, heat capacity and thermal conductivity of liquid egg products. Journal of Food Engineering;74(2):186-90.
Dix L, Van Staden J. 1981. Auxin and gibberellin-like substances in coconut milk and malt extract. Cell, Tissue and Organ Culture;1(1):239-46.
Fontan Rdci, Plant Santos LS, Bonomo RCF, Lemos AR, Ribeiro RP, Veloso C. 2009. Thermophysical properties of coconut water affected by temperature. Journal of Food Process Engineering;32(3):382-97.
Gratao ACA, Junior VS, Polizelli MA, TELIS‐ROMERO J.2004. Thermal properties of passion fruit juice as affected by temperature and water content. Journal of Food Process Engineering;27(6):413-31.
Minim LA, Telis VR, Minim VP, Alcantara LA, Telis-Romero J.2009. Thermophysical properties of lemon juice as affected by temperature and water content. Journal of Chemical & Engineering Data;54(8):2269-72.
Muramatsu Y, Tagawa A, Kasai T. 2005. Effective thermal conductivity of rice flour and whole and skim milk powder. Journal of Food Science;70(4):E279-E87.
Muramatsu Y, Tagawa A, Kasai T.2005. Thermal conductivity of several liquid foods. Food Science and TechnologyResearch;11(3):288-94.
Pereira CG, Resende JV, Giarola TMO, Pinto SM, Abreu LR. 2013.Thermal conductivity of milk with different levels of moisture and fat: experimental measures and prediction models. Semina: Ciências Agrarias;34(3):1153-66.
Rostapour OR, Joukar A, Gazor HR, Joukar L. 2011. Effect of concentrarion and temprature on the thermophysical prpperties of clarified pomegranate juice.Journal of Nutrition Science & Food Technology, Jfst No. 37, Vol 9.
Standard No. 3897, Malt extract: Characteristics and analysis, 2001, Institute of Standard and Industrial Research of Iran (ISIRI)
Tan I, Wee CC, Sopade PA, Halley PJ.2004.Estimating the specific heat capacity of starch‐water‐glycerol systems as a function of temperature and compositions. starch‐Stärke;56(1):6-12.
Tavman I, Tavman S. 1999. Measurement of thermal conductivity of dairy products. Journal of Food Engineering;41(2):109-14.
Telis‐Romero J, Gabas A, Polizelli M, Telis V.2000. Temperature and water content influence on thermophysical properties of coffee extract. International Journal of Food Properties;3(3):375-84.
Yungelson L, Han Z.2007. flow behavior and functional properties of malt extract concentrates. Journal of Texture Studies. 20,479 - 497.
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