Real time shelf-life determination of UHT milk can be very time consuming andexpensive. New procedures must be developed to predict or estimate shelf-lifes of a food product without running a full length storage trial. The aim of this study was to gain a deeper know-ledge concerning the general and accepted way of performing accelerated storage tests on diary product with oxidation as the delimiting quality failure parameter. The best oxidative indicator was the total hexanal content. The measurement method of hexanal by using GAS Chromatography (GC) together with Q10 predictive method was the procedure for indirect determination of shelf-life of UHT milk. The shelf-life was estimated to be 217 days when is styored at 25 oC, 81 days at 35 oC and 35 days at 45 oC

Gavan, Constantin

Lazar, Corina Daniela

Motorga, Vergil

Real time shelf-life determination of UHT milk can be very time consuming andexpensive. New procedures must be developed to predict or estimate shelf-lifes of a foodÂ product without running a full length storage trial. The aim of this study was to gain aÂ deeper know-ledge concerning the general and accepted way of performing acceleratedÂ storage tests on diary product with oxidation as the delimiting quality failure parameter.Â The best oxidative indicator was the total hexanal content. The measurement method ofÂ hexanal by using GAS Chromatography (GC) together with Q10 predictive method was theÂ procedure for indirect determination of shelf-life of UHT milk. The shelf-life was estimatedÂ to be 217 days when is styored at 25 oC, 81 days at 35 oC and 35 days at 45 oC

Annals of the University of Craiova - Agriculture, Montanology, Cadastre Series

Analele Universităţii din Craiova, seria Agricultură – Montanologie – Cadastru (Annals of the University of Craiova - Agriculture,Montanology, Cadastre Series) Vol. XLV 2015177STUDY ON ACCELERATED SHELF-LIFE TESTING OF UHT COW MILKLAZĂR  CORINA  DANIELA¹ ; GĂVAN CONSTANTIN²;  MOTORGA VERGIL3¹ Candidate for a doctor’s degree, Faculty of Agriculture  Craiova² Faculty  of  Agriculture  Craiova3ARDS Simnic-CraiovaKeywords: UHT milk, accelerated shelf-life test, hexanal, Q10 predictive methodABSTRACTReal time shelf-life determination of UHT milk can be very time consuming andexpensive. New procedures must be developed to predict or estimate shelf-lifes of a foodproduct without running a full length storage trial. The aim of this study was to gain adeeper know-ledge concerning the general and accepted way of performing acceleratedstorage tests on diary product with oxidation as the delimiting quality failure parameter.The best oxidative indicator was the total hexanal content. The measurement method ofhexanal by using GAS Chromatography (GC) together with Q10 predictive method was theprocedure for indirect determination of shelf-life of UHT milk. The shelf-life was estimatedto be 217 days when is styored  at 25 oC, 81 days at 35 oC and 35 days at 45 oC.INTRODUCTIONUltra high-temperature (UHT) milk is milk processed at a combination of times andtemperatures in the ranges of 130-150 oC, for 2-8 seconds and aspetically packaged toproduce a commercially sterile product. The product requires no refrigeration and has alonger self-life.Shelf-life is defined as the time during which the food product will:- remain safe;- be certain to retain desired sensory, chemical, physical and microbiologicalcharacteristics;- comply with any label declaration of nutritional data, when stored under therecommended conditions.A dairy food is inherently perishable and depending on its physical and chemicalproperties, microbiological quality and the storage conditions, there will come a point wheneither its quality will be unacceptable or it will become harmful to the consumer. At thispoint it has reached the end of its shelf-life. The ability to predict this is of great value tothe dairy industry when defining storage and distribution conditions and limits, formulatingproducts, assessing manufacturing processes and doing quantitative risk assessement.Many food-products have some variation of open shelf-life dating marked on theircontainers. These dates help the consumer to decide haw long the product may be storedprior consumption and help with stock rotation in grocery stores. Therefor foodmanufacturer conduct studies to determine the shelf-life of their product. Two methods areused: direct and indirect methods. The direct method involves storing the product underpreselected conditions for a period of time (longer than the expected shelf-life), andchecking the product at regular intervals to see when it begins to spoil.The indirect method uses accelerated shelf-life testing (ASLT) or predictivemodeling.Accelerated shelf-life testing (ASLT) offers a way to estimate shelf-life withouthaving to wait a long time for the answer.Shelf-life studies and ASLT require a profund knowledge of the constituents of thefood, the process, the microbiological safety factors, the main modes of qualitydetermination and the intended  storage condition (Mizrahi, 2004). The shelf-life of aAnalele Universităţii din Craiova, seria Agricultură – Montanologie – Cadastru (Annals of the University of Craiova - Agriculture,Montanology, Cadastre Series) Vol. XLV 2015178product depends on four main considerations: formulation, processing packaging andstorage conditions. For packaging and store conditions, the keeping properties of theproduct are function of its microenvironment. This include temperature, relative humidity,gas composition, light and pressure. Any or all of these components may be manipulatedto lengthen shelf-time.The concept of accelerated studies is to increase reaction causing factors in orderto accelerate changes in the physical, chemical or microbiological characteristics of foodproducts. Increasing storage temperature is the most popular method used. By subjectingthe food to such a controlled environment the deterioration rate will ne increased, resultingin a shorter time to product failure.Ultra high temperature (UHT) processed milk has a reported shelf-life of 6 to 9months at room temperature (25 oC). The sensory quality and the shelf-life of UHT milk isgoverned by the progression of various physic-chemical and biochemical changes afterprocessing. The main changes are due to proteolytic, lipolytic, oxidative and Maillard typereactions (Datta and Decth, 2003). Although UHT processing inactivates most bacteria,some heat-stable enzymes of native and bacterial origin can survive and cause shelf-lifelimiting defects. Proteolysis is associated with release of tyrosine thet contribute to thedevelopment of off-flavours. The B-lactoglobulin-K-casein complexes during heattreatment increase the viscosity of milk (Datta and Decth, 2003).Lypases can hydrolyse triacylglycerols with the release of  medium and short chainfatty acids. Rancidity and off flavours can occur if triglyceride contains volatile, short fattyacids mainly butyric acid (C4:O) and lauric acid (C12:O) as in dairy fats.The same hydrolytic rancidity mechanism can be a result when triglycerides areexposed to water. Water hydrolyses and split the ester bonds, breaking the structure oftriglycerides into mono or diglycerides and free fatty acids (FFA). This reaction is catalyzedby either high temperature or due to the enzyme lipase or a combination of bouth (Sewaldand DeVries, 2003). The amount of FFA can be measured but in not a true measure of thereaction rate.The oxidative rancidity reaction is a spontaneous reaction of unsaturated fatty acidswith atmospferic oxygen (Coultate, 2009). The reaction can be accelerated at highertemperatures (Shahidi and Wiley, 2005). The reaction requires some initial activationenergy in order to remove a hydrogen atom from unsaturated fatty acid (UFA). Highertemperatures and the presence of double bonds enabled this (Barriuso et al, 2013).Also oxygen reacts with a double bound on an UFA resulting hidroperoxides andradicals. Further oxidation steps lead to the breakdown of hydroperoxides and productionof carbonyl compounds such as aldehydes. Identification of these secondary oxidationproducts has a great significance. The perception of rancidity is often due to this amount ofvolatile aldehides such as propanal, pentanal, hexanal, heptanal and nonanal (Barriuso,2013). Hexanal is the most important volatile degradation compound, deriving fromchemical oxidative rancidity mechanism, and is created from 13-hydroperoxidisomerderivative (Coultate, 2009). If free oxygen attacks for example carbon number 13 on thefatty acid molecule it results in the formation of a 13 hidroperoxides, Linoleic acid (C18:2)gives rise to the formation of 9-13-hidroperoxidis.Hexanal is more frequently measured as it formation is higher than of othersecondary oxidation products (Barriuso et al, 2013).The aim of this study was to gain a deeper knowledge concerning the general andaccepted way of performic accelerated storage test on dairy product with oxidation as thedelimiting quality failure parameter.Analele Universităţii din Craiova, seria Agricultură – Montanologie – Cadastru (Annals of the University of Craiova - Agriculture,Montanology, Cadastre Series) Vol. XLV 2015179MATERIALS AND METHODSExperimental designThe concentration and quantity of n-hexanol in low fat UHT milk can be detected in10 minutes by the GasCromatography/MS (GC/MS) analysis.The sample must be kept cold to minimize the risk for oxidation before analysis.Acording to Sewald and DeVries, 2003, a homogenous portion of the sample must becollected, and at least six samples should be analized at the test temperature within arange of 20-60 oC. The formation of primary and secondary oxidation products wereobserved between 25 and 75 oC, according to the literature. Common test temperature are10 oC apart (e.g. 20, 30, 40 and 50 oC). It is preferable a control sample, stored to 0 oC.Analysis each weck is commonly performed and each testing temperature should have atleast six data points over time to make the study results statistically reliable. At least twotemperature are required, but three or four is an ideal number for more precise predictionsof shelf-life (Hough et al, 2006). A test temperature over 50 oC in not good, n-hexanal canbe converted to hexanoic acid or to n-hexanol at higher pH by alcohol dehydrogenase withsmall impact on sensory attributes in food products (Mellor et al., 2010).According to the literature a shelf-life study concerning oxidative stability could becarried out for 60 days to generate good test results.Sample preparation and analysis methodFor this study milk from three different batches (3 replicates) of low fat UHT milkwas collected on the day of production and stored at 25, 35 and 45 oC for 210 days. Thegross composition (protein, lactose and fat content), microbiological quality(Enterobacteriaceae level) and volatile aldehyde compounds were analysed by theSanitary Veterinary and Food Safety Laboratoriers Timisoara and Dolj.The analysis of variance was performed to identify differences in gross compositionof milk and microbiological quality and also to identify any changes over time (0, 30, 60,120, 150, 180 and 210 days). Volatile aldehyde components were extracted by solid phasemicro extraction (SPME) and were analysed by GC/MS.A homogenous portion of the sample is suspended and mixed with boilig watercontaining an internal standard (4-heptanone). The sample is then heated for a specifiedamount of time. Then a sample of the headspace is taken and injected into GC analyzer.The hexanal released is detected and quantified via comparasion of the internal standard.Kinetic mathematical modelsShelf-life prediction is based on reaction kitecics where the acceleration of thedeterioration rate is direct time and temperature depended. The quality loss follows theequation dQ/dt = K(QA)n, where dQ/dt is the change in the measurable qualiry factor A,with time, K is the rate constant in appropriate units, and n is the order of the chemicalreaction of the quality factor. The order of reaction for most quality attributes in foodproducts is either zero, first or second. Rancidity reactions are first under reaction since itis degradation reactions. The rate of quality decrease is exponential. Plotting the log scalevalues versus time, makes the experimental data easily interpretable.The rate constant (K) from the liniar relationship can be determined:= ; lnK = lnK0 - , where:K = a reaction rate constant to be estimated;K0 = a constant independent of temperatureEA = activation energy (Kcal/mol) specific for a certain reaction;R = is the molar gas constant 8.31 J/K/mol;T = temperature (in oKelvin).Analele Universităţii din Craiova, seria Agricultură – Montanologie – Cadastru (Annals of the University of Craiova - Agriculture,Montanology, Cadastre Series) Vol. XLV 2015180Once the K value, the slope, is determined, the activation energy (EA) can bedetermined using Arrhenius equation.Arrhenius equationA chemical deterioration process require a certain amount of energy to get startedand this is called the activation energy (EA) given in Kcal/mol. If the temperature getshigher, the acceleration of the reaction will increase. The reaction rate constant Kquantifies the speed of the reactive. In a first order reaction, EA should result in a plot ofthe lnK and the reciprocal of temperature, 1/T, generating a slope. The data can beextrapolated further in order to find out the oxidative rate for a desirable temperature or tofind the accelerating factor.Q10-modelingQ10 is the increase in the rate of the reaction when the temperature is increased by10 oC.The Q10- value of 2 is usually found for enzymatically induced changes ordegradation of pigments and flavors. The Q10- value can also be calculated from the ratiobetween the rate constant at KT and KT+10. This means in practice that themeasurements (in mg of hexanal per 1000 g sample) can be used directly.Q10 = = ℃KT + KT + 10 = recation rate constants at temperature T + T + 10 oC;T and T + 10 = temperatures;ST + ST + 10 = related shelf-life estimates at temperature T and T + 10.Accelerating factorAccelerated shelf-life tests are needed to find a proper acceleration factor (AF) forthe tested product.Arrhenius equation and Q10- modeling method are mainly two possible procedures.The EA is the information needed to determine the AF. The AF enables the conversionfrom accelerated temperature is back again to actual storage condition at normaltemperatures.AF = exp −AF = accelerating factor;exp (x) = ex;Tu = actual storage temperature;Ttest = accelerated test temperature.RESULTS AND DISCUSSIONThe freshly packed low fat UHT milk used showed satisfactory milk composition andmicrobiological quality (Table 1).Table 1Milk composition and microbiological quality of freshly packed UHT milkBatch 1 Batch 2 Batch 3Milk composition% fat (g/100g)% protein (g/100g)% lactose (g/100g)1,80 ± 0,023,48 ± 0,024,95 ± 0,01 1,81 ± 0,023,50 ± 0,024,91 ± 0,02 1,82 ± 0,023,49 ± 0,024,90 ± 0,01Microbiological quality:Enterobacteriaceae CFU/ml < 1 < 1 < 1The mean content of fat, protein and lactose was 1,81 ± 0,01, 3,49 ± 0,01 and 4,92± 0,02% (Bath 1 + Bath 2 + Bath 3).Analele Universităţii din Craiova, seria Agricultură – Montanologie – Cadastru (Annals of the University of Craiova - Agriculture,Montanology, Cadastre Series) Vol. XLV 2015181The microbiological quality of the UHT milk was very high with counts of < 1CFU/ml. The microbiological quality was maintained trroughout the duration of the study atambient temperature (Table 2).Table 2The effect of storage time on microbiological quality of UHT milkEnterobacteriaceaeTime (days) 0 30 60 120 150 180 210Batch 1 (CFU/ml) < 1 < 1 < 1 < 1 < 1 < 1 < 1Batch 2 (CFU/ml) < 1 < 1 < 1 < 1 < 1 < 1 < 1Batch 3 (CFU/ml) < 1 < 1 < 1 < 1 < 1 < 1 < 1Hexanal content showed the most change over the time period. Regression curvesand R-squared:at 25 oC: Y = 0,07x + 13,26R2 = 0,876at 35 oC: Y = 0,27x + 13,93R2 = 0,912at 45 oC: Y = 0,64x + 49,15R2 = 0,840Hexanal content is suitable for estimating the shelf-life parameters. Hexanalparameters for UHT milk are presented in Table 3.Table 3Hexanal parametersTemperature(oC)Rate constant KHexanal score/dayCoefficient ofdetermination (R2)Acceleration factor25 – 35 oC 35 – 45 oC25 oC35 oC45 oC0,13800,37140,86660,8760,9120,8403.97 2.57Shelf-life of UHT milk stored at 35 oC and 25 oC was estimated at 81 days and 217days, respectively.The acceleration factor was determined to be 3,97 and 2,57 when the storagetemperatures increased from 25 oC to 35 oC and from 35 oC to 45 oC, respectively. Therate of oxidative deterioration of the milk at 35 oC will be more than 3,9 times faster, andthe rate at 45 oC will be 10,2 times faster, than rate at 25 oC. This means that, for onestimated shelf-life of 217 days, future hexanal in ASLT have to be conducted for 81 daysat 35 oC or only 35 days at 45 oC.CONCLUSIONSThe hexanal content in accelerated shelf-life test was successfully applied to low fatUHT milk. The shelf-life of the designated low fat UHT milk was estimated to be 217 dayswhen is stored at 25 oC.Higher temperatures of storage negatively affected the shelf-life of UHT milk. Shelf-life was shortered to 81 days and 35 days, when is stored at accelerated temperature of35 oC and 45 oC, respectively.An accelerated shelf-life study should always be performed in parallel with a full-length study and with sensory evaluation program. The sensory evaluation program isconsidered as major limiting parameter, due to the consumers acceptance.Analele Universităţii din Craiova, seria Agricultură – Montanologie – Cadastru (Annals of the University of Craiova - Agriculture,Montanology, Cadastre Series) Vol. XLV 2015182REFERENCES1. Barriuso, B., Astiasaran, I., Ansorena, D., 2013 – A review of analytical methodsmeasuring lipid oxidation status in foods: a challenging task, (Electronic) European FoodResearch and Technology, Volume 236, p. 1-15, Available: http://link.springer.comarticle/10.1007/S00217-012-1866-9 (2015 02 22)2. Coultate, T.P., 2009 – Food – the chemistry of its components, fifth edition, RSCPublishing, page: 115-1223. Datta, N, Deeth, H.C., 2003 - Daignosing the cause of proteolysis in UHT milk, FoodScience and Technology, 36: 173-1824. Hough, G., Garitta, L., Gomez, G., 2006 – Sensory shelf-life predictions by survivalanalysis accelerated storage models, Food quality and Preference, vol. 17, page: 447-468,(Electronic): http:///www.sciencedirect.com/science/article/pii/so950329305000856 (2015-8-13)5. Mellor, N, Bligh, F., Chandler, I., Hodgman, C., 2010 – Eduction of Off FlavorGeneration in soy bean Homogenates, A Matheematical Model (Electronic) Journal ofFood Science, vol. 75, pages: R131-R138; http://onlinelibrary.wiley.com/doi/10.1111/J1750-38412010.01733.x/full (2015-3-5)6. Mizrahi, S., 2004 – Accelerated shelf-life tests in Understanding and Measuring theshelf-live of food, Woodhead publishing limited, Cambridge, England 2004, https:// books.google.ro/books?id7. Sewald, M., DeVries, J., 2003 – Food product shelf-life, Medallion Laboratories,Minesota, US (Electronic Brochure), http:// www. Medlab.com/TechnicalPublications.aspx.(2015 03 20)8. Shahidi, F., Wiley, J., 2005 – Bailey’s Industial Oil and Fat Products, Sixth edition,John Wiley and Sons, Lipid oxidation chapter 8, Memorial University of NewfoundlandCanada, Electronic, available: Knovel, (2015-01-30)

STUDY ON ACCELERATED SHELF-LIFE TESTING OF UHT COW MILK

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STUDY ON ACCELERATED SHELF-LIFE TESTING OF UHT COW MILK

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Annals of the University of Craiova - Agriculture, Montanology, Cadastre Series