Optimization of Pasteurization Machine Level Settings with Heat Transfer Fluid and Pulsed Electric Field Technology Based on Randu Honey Quality Testing

. Randu honey is a type of monofloral honey produced by bees that consume nectar from randu flowers. Randu honey has a high water content because the flowering process occurs at night with high humidity. This research aims to determine the optimal parameter level settings in the pasteurization process of randu honey using a pasteurization machine regarding the parameters of heating temperature in the HTF, voltage at PEF, stirring speed in the tube, and PEF process time. Experiments were carried out using Response Surface Methodology (RSM) which was applied to determine the exact values of optimal process parameters that simultaneously compromise all responses. Based on the experimental results, the results of multi-objective optimization obtained optimal process parameters that can be applied to the machine is HTF temperature factor of 60°C, voltage at PEF 25kV, stirring speed in the tube 30 rpm, PEF process time 120 minutes.


I. INTRODUCTION 1
Honey is one of the superior forest products besides wood originating from Indonesia.In 2021, Indonesia will be able to produce 189,780 liters of honey with the largest production area being on the island of Java (BPS, 2021).However, honey produced by Micro, Small, and Medium Enterprises (MSMEs) is mostly low-quality due to a lack of post-harvest equipment support (KSDAE, 2017).
The main requirements for commercial honey must contain a diastase enzyme of at least 3 DN (diastase number), a maximum microbial content of 100 CFU/g, a maximum acidity level of 50 ml NaOH/kg, a maximum hydroxymethylfurfural (HMF) content of 40 mg/kg, and a maximum water content of 22% (SNI 8664:2018).If honey is processed using a thermal process at temperatures above 71ºC, it allows the nutritional content of the honey to be degraded and caramelization occurs (Skinner, 2019).Wibowo, et al. (2022) explained that high HMF values due to thermal processes result in low DN values which affect the honey content.Therefore, it is important to develop non-thermal pasteurization technology for food preservation that can inactivate microbes and maintain honey quality (Arshad et al., 2021).
Non-thermal pasteurization aims to reduce microbial contamination of food contents (IFT, 2020).Galanakis (2018) stated that the appropriate non-thermal pasteurization technology to be applied to MSME honey farmers in Indonesia is Pulsed Electric Field (PEF).PEF technology has the advantage of being used to process honey with a capacity of under 150 liters, does not require a lot of cost, and the equipment is easy to use (Fua'ida, 2015;Hariono, 2010).Nonthermal pasteurization uses an electric shock to reduce the amount of mold and yeast in honey without changing the taste or smell.
According to Chasanah (2001) and Evehalda (2015), there are types of yeast that can grow in conditions of low pH and high sugar concentration, causing the honey fermentation process to occur.The fermentation that occurs in honey is caused by the high water content of honey.The water content in honey can trigger the growth of mold and yeast which can damage the quality of the honey.
One type of honey that has a high water content is randu honey.According to Harno (2016), randu honey has a thinner viscosity than honey from other flowers because randu honey has a high water content.The high water content in randu honey is because the randu tree has a nocturnal flowering period so honey bees collect nectar at night which has low temperatures and high humidity.
Honey fermentation is caused by a type of osmophilic yeast from the genus Zygosaccharomyces, resulting in a decrease in the quality of honey, a decrease in nutritional value, and a decrease in the shelf life of honey (Illyya, Haryanti, & Suedy, 2017).Yeast activity can be inhibited by minimizing the water content of honey through the heating process (Howse, 2018).However, heating honey to high temperatures during the pasteurization process can cause an increase in HMF concentration, which is an indication of honey damage.High concentrations of HMF trigger cell and DNA damage, are mutagenic, carcinogenic, and cytotoxic so they are not consumed in large quantities (Meli et al., 2018).
Several pasteurization parameters applied include parameters voltage at PEF, temperature, stirring speed, and process time.Each applied parameter has several levels.This process uses temperature levels consisting of 24°C and 60°C.The temperature level of 24°C is room temperature or the minimum temperature which aims to maintain the content of HMF and diastase enzymes.The temperature level of 60°C in the HTF process is the maximum level limit.If honey is heated to more than 60°C it becomes unstable and thermolabile which has an impact on reducing the diastase number (DN) and its nutritional content (Razali, 2018).
The voltage levels on the applied PEF include 25, 30, and 35kV.The recommended voltage level setting on the PEF is 30kV with a pulse frequency of 20 KHz (Vadlamani et al., 2020).Set the PEF voltage at 25kV and 35kV to determine the effect of a voltage difference of 5kV on the content of randu honey.Apart from that, the PEF voltage setting of 35kV is the maximum voltage limit on the pasteurization machine.Stirring speed level settings include 20, 25, and 30rpm.
The selection of the stirring speed setting of 25rpm is based on calculating the angular speed, fluid speed, and the rotation period of the stirrer propeller on the elasticity of the honey stirrer to avoid spills and the risk of caramelization.Stirring speed settings of 20rpm and 30rpm were used to determine the effect of a difference in stirring speed of 5rpm on the content of randu honey.
In this research, all process parameters are a combination of several pasteurization processes for randu honey.Optimization of parameter settings by considering four responses simultaneously is used to sterilize honey, increase shelf life, and maintain the smell and taste that are characteristic of honey.Response Surface Methodology (RSM) was chosen to estimate the level of pasteurization process parameter settings as a new proposal that is easy to implement on factors with few levels.Combination of factors with continuous values using RSM in optimizing parameter settings in the pasteurization process of randu honey including temperature at HTF, voltage at PEF, stirring speed in the tube, and PEF process time to reduce mold and yeast levels, water content, HMF, and increase enzyme activity diastase.

II. RESEARCH METHOD
This research was conducted at the Production Planning and Design Laboratory, Industrial Engineering Department, Faculty of Engineering, Sebelas Maret University.First, we defined the responses, factors, and levels of this research.The response in this research was the quality of pasteurized randu honey which included mold and yeast content, water content, HMF, and diastase enzyme activity value.This research considered four factors, including heating temperature in the HTF, voltage in the PEF, stirring speed in the tube, and PEF processing time.Table 1 shows the factors and their respective levels.
These four parameters were combined to produce 30 types of treatment.Table 2 is sample data from the honey pasteurization testing process using a PEF machine.
In this research, honey was tested using nonthermal PEF pasteurization technology using a pasteurization machine designed according to honey testing needs.The pasteurization machine frame is made of aluminum extrusion with a tube that can hold 80 liters, has a 600W electric heater and the PEF intensity is regulated via an analog system for PEF modulation.
The PEF pasteurization machine used for processing honey in this research is shown in Figure 1.

Response Surface Methodology
Response surface methodology (RSM) is a method developed for response models (y) with more than one factor variable.RSM aims to optimize responses by modeling and analyzing responses that are influenced by several variables (Montgomery, 2001).The equation model for each response in determining the optimal level setting in this research is a regression model using Minitab 2018 software.
An experiment that uses k factors X1, X2, ..., Xk with Y the response variable.The variables used can be measured and it is known that Y is partially or completely a response to X1, This is a response surface where for k=1 we get Y = f(X) which is called the response line.In determining the response surface equation, several models have been formulated so that the experiments carried out can be as close as possible to the equation.In terms of two dimensions, the first order and second order response equations are shown in equations ( 1) and ( 2). (1) (2)  The interaction relationship between controlled factors and noise factors is one of the keys to a strong design.So we need a logical model of a response that includes these two factors with equations is (3) The model above has the main influence of these two factors which is usually called the model response.Myer and Montgomery ( 2001) describe a multi-response method called desirability.Desirability is an objective function from the limit 0 to 1.For several responses and all level factors it is intended to be combined into a desirability function, D(x) with the equation where n is the number of responses analyzed.For optimization, each response must have a high and low value with a maximum -minimum goal value, target or within a certain range.

III. RESULT AND DISCUSSION
The pasteurization process of randu honey is carried out using a pasteurization machine with heat transfer fluid (HTF) and pulsed electric field (PEF) technology.In this research, there were four test responses that influenced the quality of randu honey, including testing the number of molds and yeasts, water content, HMF, and diastase enzyme activity.
Based on the pasteurization test of randu honey which was carried out using a pasteurization machine with PEF technology, a sample of honey pasteurization results was obtained as shown in figure 2.
From the results of the tests that have been carried out, it shows that samples of randu honey that have not been processed using HTF and PEF contain mold and yeast numbers above 1 x 102 colonies/g (do not meet SNI for honey).This proves that the combination of HTF and PEF provided is able to inactivate the maximum number of molds and yeasts.
Randu honey processed at a heating temperature of 24°C has a higher water content than that processed at a temperature of 60°C.
This proves that heating temperature can reduce the water content due to the evaporation process.Apart from that, randu honey processed with a stirring speed of 20 rpm has a lower water content than 30 rpm.This happens because the stirring process can evenly distribute the heating temperature throughout all parts of the honey without causing the release of excess heat due to the speed of the stirring rod.Randu honey processed at a heating temperature of 24°C tends to have a lower HMF content than that processed at a temperature of 60°C.Apart from that, honey processed with a PEF voltage of 35kV within 240 minutes also produces higher HMF content.This is because the higher heating temperature, PEF voltage, and longer processing time given in processing honey can trigger an increase in glucose degradation, thereby increasing the HMF content in honey.
Randu honey processed without pasteurization has a higher diastase enzyme value compared to that processed using HTF and PEF.The higher the heating temperature and the PEF voltage applied can damage the enzyme cell walls which results in the value of the diastase enzyme in honey decreasing.Apart from that, slower stirring speeds and longer processing times also cause a decrease in the diastase value because the heat and electric voltage received by all parts of the honey are evenly distributed.
A summary of the fit and ANOVA output of the response to mold and yeast numbers was carried out by testing the model on two equations, linear and quadratic for each response.Table 4 contains the results of processing response data mold and yeast numbers with RSM method using Minitab 2018.
The data is visualized using a contour plot as in Figure 3 and a response surface plot of mold and yeast numbers as in Figure 4 which shows the response of each parameter.
Table 5 contains the results of processing water content response data with RSM method using Minitab 2018 software.To make it easier to see the results of the discussion based on the resulting equations, the data is visualized using a contour plot as in Figure 5 and a response surface plot of water content as in Figure 6 which shows the response of each parameter.
Table 6 contains the results of processing HMF response data with RSM method using Minitab 2018 software.
To make it easier to see the results of the discussion based on the resulting equations, the data is visualized using a contour plot as in Figure 7 and a response surface plot of HMF as in Figure    8 which shows the response of each parameter.Table 7 contains the results of processing diastase enzyme activity response data with RSM method using Minitab 2018 software.
Based on the resulting equations, the data is visualized using a contour plot as in Figure 9 and a response surface plot of diastase enzyme activity as in Figure 10 which shows the response of each parameter.
After processing the data using RSM, the most optimal desirability value was obtained at 0.6274 with a HTF temperature factor of 60°C, a voltage at the PEF of 13kV, a stirring speed in the tube of 30 rpm, and a PEF processing time of 34 minutes.However, a PEF voltage of 13kV cannot be applied to a pasteurization machine due to  Therefore, desirability is re-determined as an optimal value that has been adjusted to the capabilities of the pasteurization machine.The optimal desirability value that has been adjusted is 0.4138 at a HTF temperature factor of 60°C, voltage at PEF 25kV, stirring speed in the tube of 30 rpm, and PEF process time of 120 minutes.
Based on the comparison of the two response optimizations using RSM, different desirability values were obtained.This difference in desire is due to the greater the PEF voltage and the longer the PEF processing time, which has an impact on increasing the HMF value.This happens because there is a combination of the HTF and PEF processes which can increase glucose degradation thereby increasing the HMF value.A high HMF value in honey will reduce the quality of honey because the HMF content is related to several other chemical properties of honey such as water content, pH, free acid content, reduced sugar content, and enzymatic activity in honey (Kowalski et. al., 2013).

IV. CONCLUSION
The optimal level setting desirability value using the RSM method in the first response test is 0.6274 with the optimal level setting at a HTF temperature factor of 60°C, a voltage on the PEF of 13kV, a stirring speed on the tube of 30 rpm, and a PEF process time of 34 minutes.
The optimal level setting desirability value using the RSM method in the second response test is 0.4138 with the optimal level setting at a HTF temperature factor of 60°C, a voltage on the PEF of 25kV, a stirring speed on the tube of 30 rpm, and a PEF process time of 120 minutes.
The level setting in the first response test cannot be applied in the pasteurization machine due to limited machine capabilities.Therefore, the machine level setting that is possible to apply is in the second response test with an optimal desirability value of 0.4138

Figure 5 .
Figure 5. Contour Plot Response Water Content

Table 1 .
Setting Factor Levels for Randu Honey

Table 2 .
Data Sample Randu Honey

Table 3 .
Response Results of Randu Honey

Table 4 .
ANOVA of Mold and Yeast Number Responses ANOVA for Response Mold and Yeast Number Figure 3. Contour Plot Response Numbers of Mold and YeastFigure 4. Response Surface Plot Numbers of Mold and Yeast

Table 5 .
ANOVA of Water Content Responses

Table 6 .
ANOVA of HMF Responses

Table 7 .
ANOVA of Diastase Enzyme Activity Responses

Table 8 .
Model Summary