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Abstract [Objectives] This study was conducted to screen best process parameters for making Foshou yam and honey can.
[Methods] The Foshou yam produced from Wuxue was used as a raw material to prepare Foshou yam and honey nutritional can by combining Foshou yam with honey through screening， pre-cooking， filling， exhausting， cooling and other technical processes. The optimum technology parameter of Foshou yam and honey nutritional can was studied through single factor tests and response surface optimization.
[Results] The optimum technical parameters of Foshou yam and honey nutritional can were citric acid concentration 0.1%， amount of edible salt 0.1%， cooking time 14 min and honey concentration 26%. Under these conditions， the final sensory score was 90.20. The prepared can was not only rich in nutrition， but also had good flavor and taste.
[Conclusions] This study provides reference for the development and utilization of Foshou yam and the research and development of functional food.
Key words Foshou yam; Honey; Can; Single factor experiment; Response surface method
Received： August 12， 2020 Accepted： Ocotber 20， 2020
Supported by 2018 Undergraduate Innovation and Entrepreneurship Training Program of Huanggang Normal University （201810514045）; High-level Cultivation Project of Huanggang Normal University （201816703）.
Siying CHEN （1999-）， female， P. R. China， major： food science and engineering.
*Corresponding author. E-mail： 843076915@qq.com.
Foshou yam is a local national geographical indication product in Wuxue， which is rich in fiber and will produce a feeling of fullness after consumption. It has an antiobesity effect， and can be said to be a delicacy with the effects of prolonging life for consumers who are pursuing green and healthy[1-2]. Foshou yam is a famous Chinese medicinal material. The medical sage Li Shizhen proposed in Compendium of Materia Medica that it has the functions of treating various deficiency， treating exhaustion or lesion of the five internal organ and seven damages， removing wind in head， relieving low back pain， eliminating dysphoria with smothery sensation， and tonifying heat-qi[3]. Foshou yam has a very low soluble sugar content， and is rich in 17 kinds of amino acids and a variety of trace elements. It is high in nutrition and low in calories， and is a good food material for lowering blood sugar， lowering blood pressure， resisting tumor， and strengthening immunity. It is the king of yam for food supplements， and has the reputation of "Dabie Mountain Ginseng"[4]. Honey has many functions such as maintaining beauty and keeping young， resisting bacteria and inflammation， promoting digestion， improving sleep， protecting liver， moistening lungs and expelling phlegm to arrest coughing， clearing damp， promoting urination， calming the mind， clearing away heat and toxic materials， and relaxing bowel[5]. Wuxue Foshou yam is loved by more and more people because of its unique taste and nutritional value. However， due to the poor storage resistance of Foshou yam， it is prone to browning[6]， resulting in seasonality and short sales time. Taking into account the high nutritional value of Foshou yam and honey and few reports on the research of Foshou yam and honey can[7]， we prepared a kind of Foshou yam honey nutrition can using Foshou yam and honey as the main raw materials after screening， pre-cooking， filling and exhausting， cooling and other processes， determined the best values of citric acid concentration， salt addition， pre-cooking time and honey concentration through single factor test and response surface optimization[8]， and screened out the optimal process parameters for production of Foshou yam and honey can. This study improved the sensory quality of Foshou yam and honey can， which meets consumer’s demand and provides reference for the development and utilization of Foshou yam and the research and development of functional foods.
Materials and Methods
Materials and Instruments
Foshou yam， salt： commercially available; Guanshengyuan honey： Shanghai Guanshengyuan Bee Products Co.， Ltd.; citric acid （food grade）： Zhengzhou Cangyu Food Chemical Co.， Ltd.; calcium chloride （food grade）， sodium D-isoascorbate （food grade）： Henan Wanbang Industrial Co.， Ltd.
Peeling knives， cutting boards， knives， induction cookers， glass jars： commercially available; electronic balance （CP413）： Ohaus Instruments （Changzhou） Co.， Ltd.
Experimental methods
Foshou yam screening→peeling→cutting→color protection→pre-cooking→rinsing→canning→soup injection→exhausting→sealing→sterilization→cooling[6， 9， 10].
① Color protection： Since the peeled Foshou yam is prone to browning， the peeled Foshou yam was quickly put into a composite color protection solution prepared by citric acid 1.5 g， calcium chloride 0.5 g and D-sodium erythorbate 0.8 g to protect the color for 30 min， so as to prevent browning of Foshou yam.
② Pre-cooling and rinsing： The yam subjected to color protection was put into boiling water for pre-cooking until the yam was fully cooked， and the pre-cooked yam was quickly put into cool water to cool it， wash away the color protection solution on the surface of Foshou yam and further rinse off small pieces of yam.
③ Soup injection： The soup in this step was prepared by mixing citric acid， salt， honey and boiled pure water. ④ Sterilization and cooling： The boiling water temperature was heated to 100 ℃， and sterilization was performed for 5 min. Cooling meant to put the cans in cooling water to cool and then wipe off the water remaining on the surface of the cans， and finally put them in a refrigerator for 2-3 d.
Sensory evaluation standard of Foshou yam and honey nutritional can
The sensory evaluation method adopted a hundred-point system. 29 experts with sensory evaluation experience were selected to score the four items of color， shape， flavor， and taste of canned Foshou yam honey to select the best technological formula. The sensory evaluation standards are shown in Table 1[6，10].
Design of single factor tests
The effects of citric acid concentration， salt addition， pre-cooking time and honey concentration on the sensory quality of Foshou yam and honey can were to be explored. With other three factors set as fixed values， the citric acid concentration （0.06%， 0.08%， 0.10%， 0.12%， 0.14%）， salt addition （0.05%， 0.10%， 0.15%， 0.20%， 0.25%）， pre-cooking time （8， 10， 12， 14， 16 min） and honey concentration （20%， 22%， 24%， 26%， 28%） were changed for single factor experiments.
Response surface analysis
On the basis of single factor tests， the sensory evaluation score （Y） was used as the response value of the investigation， and the concentration of citric acid （A）， salt addition （B）， pre-cooking time （C）， and honey concentration （D） were used as the investigation factors. The Box-Behnken in Design-Expert software was used to design a four-factor three-level test， and the response surface methodology was used to optimize the best process parameters of Foshou yam and honey can.
Results and Analysis
Results and analysis of single factor tests
Effect of citric acid concentration on the sensory quality of Foshou yam and honey can
The effect of citric acid concentration on the sensory quality of Foshou yam and honey can is shown in Fig. 1. It can be seen from Fig. 1 that with the increase of citric acid concentration， the sensory score of Foshou yam and honey can showed a trend of first increasing and then decreasing. When the concentration of citric acid was 0.10%， the sensory score of Foshou yam and honey can was the highest. Meanwhile， the taste of the canned food was soft and glutinous， sour and sweet， and when the concentration of citric acid continued to increase， the sourness of Foshou yam and honey nutritional can increased and the sensory score decreased. It can be obtained that the optimal citric acid concentration was 0.10%， so 0.08%， 0.10% and 0.12% were selected as the three levels of citric acid concentration. Effect of salt addition on the sensory quality of Foshou yam and honey can
The effect of salt addition on the sensory quality of Foshou yam and honey can is shown in Fig. 2. It can be seen from Fig. 2 that as the amount of salt added increased， the sensory score first increased and then continued to decrease. When the amount of salt added was 0.10%， the sensory score reached the highest score. Adding too much salt reduced the sweetness of the can and made the flavor worse. It can be obtained that the optimal amount of salt was 0.10%， so 0.05%， 0.10% and 0.15% were selected as the 3 levels of salt added.
Effect of pre-cooling time on the sensory quality of Foshou yam and honey can
The effect of pre-cooking time of Foshou yam on the sensory quality of Foshou yam and honey can is shown in Fig. 3. It can be seen from Fig. 3 that with the increase of the pre-cooking time， the sensory score first continued to increase and then decreased. When the pre-cooking time was 14 min， the sensory score reached the highest， indicating that the sensory index of Foshou yam and honey can reached the best， and it was easy to be accepted. It can be concluded that the optimal pre-boiling time was 14 min， so 12， 14 and 16 min were selected as the 3 levels of the pre-cooking time of Foshou yam.
Effect of honey concentration on the sensory quality of Foshou yam and honey can
The effect of honey concentration on the sensory quality of Foshou yam and honey can is shown in Fig. 4. It can be seen from Fig. 4 that as the honey concentration increased， the sensory score first increased and then decreased. When the honey concentration increased to 26%， the sensory score reached the highest， which showed that the honey concentration of 26% was the sweetness easy to accept. It can be obtained that the optimal honey concentration was 26%， so 24%， 26% and 28% were selected as the 3 levels of honey concentration.
Results and analysis of response surface analysis test
Factor level selection
Combining the above single factor test results， with the sensory score of Foshou yam and honey can as the response value （Y） and citric acid concentration （A）， salt addition （B）， pre-cooking time （C）， and honey concentration （D） as factors， the Box-Behnken of the Design-Expert 8.0.6 software was used to design a four-factor three-level response surface optimization test， and a prediction model required for response surface test analysis was established. The factor levels are shown in Table 2[7]， the experimental design and results are shown in Table 3. Analysis of response surface test results
Data in Table 3 was subjected to analysis of variance to get a quadratic polynomial regression model： Sensory evaluation=+89.98-0.050A-0.075B+0.067C-0.33D-0.45AB-0.28AC-0.13AD+0.58BC-0.35BD+0.40CD-1.57A2-2.06B2-1.39C2-2.28D2. The regression analysis of variance is shown in Table 4.
The results of the variance analysis of the response surface regression model are shown in Table 4. From Table 4， we can see that： the model P<0.000 1 indicated that the response surface regression model reached an extremely significant level; P value of the lack of fit term was 0.895 7>0.05， which was not significant， indicating that the regression model could well fit the actual measured values; the correlation coefficient R2=0.959 1 indicated that the test error was small and the model fit well; and the adjusted correlation coefficient R2Adj=0.918 1 indicated that the model could explain 91.81% of the change in the response value， and the model could be used to predict and analyze the processing conditions of Foshou yam and honey can[7，11]. The F value can reflect the effects of various factors on test results， and the value of the F value was directly proportional to the effect[12-13]. It can be seen from Table 4 that the effects of the four factors on the sensory quality of Foshou yam and honey can be D （concentration of honey）>B （addition of salt）>C （pre-cooking time）>A （concentration of citric acid）. In the model， the one degree term D had a significant effect on the sensory evaluation of Foshou yam and honey can （P<0.05）， and other one degree terms had no significant effect; the interaction item BC had a significant effect （P<0.05）， and other interaction items had no significant impact; and the effects of the quadratic items A2， B2， C2 and D2 were all extremely significant （P<0.000 1）.
Response surface analysis of multi-factor interaction
Fig. 2 visually shows the response values and contour analysis diagrams of interaction between various factors. The flatter the edge of each factor in the figure， the smaller the effect of the factor on the sensory score， and the steeper the edge of the factor， the greater the effect of the factor on the sensory score[14]. Fig. 2（A） shows that when the pre-cooking time was 14 min and the honey concentration was 26%， the increase in citric acid concentration was smaller than that of salt， indicating that among the sensory effects on Foshou yam and honey can were in order of B>A. Fig. 2（B） shows that when the honey concentration was 26% and the salt addition was 0.10%， the citric acid concentration increased less than the pre-cooking time， indicating that the sensory effect on Foshou yam and honey can were in order of C>A. Fig. 2（C） shows that when the concentration of citric acid was 0.10% and the concentration of honey was 26%， the increase in pre-cooking time was smaller than the amount of salt added， indicating that the sensory effects on Foshou yam and honey can showed an order of B>C. Fig. 2（d） shows that when the pre-cooking time was 14 min and the citric acid concentration was 0.10%， the increase in salt addition was smaller than honey concentration， indicating that the sensory effects on Foshou yam and honey can were in order of D>B. Fig. 2（e） shows that when the concentration of citric acid was 0.10% and the amount of salt was 0.10%， the pre-cooking time increased less than the honey concentration， indicating that the sensory effects on Foshou yam and honey can exhibited an order of D>C. Fig. 2（f） shows that when the salt addition was 0.10% and the pre-cooking time was 14 min， the increase in citric acid concentration was smaller than that of honey， indicating that the sensory effects on Foshou yam and honey can were in order of D>A. Verification results
Through the prediction of the regression model， under the parameters of citric acid concentration 0.10%， salt addition 0.10%， pre-cooking time 14.03 min， and honey concentration 25.86%， the sensory evaluation score of Foshou yam and honey can was the highest. In consideration of the operability of the experiment， the process parameters were adjusted to citric acid concentration 0.10%， salt addition 0.10%， pre-cooking time 14.00 min， and honey concentration 26.00% in the actual experiment. On this basis， three sets of parallel verification experiments were carried out， and finally， the sensory score of Foshou yam and honey can was 90.20±0.58， which was close to the predicted value， indicating that the model was reliable and had certain practical guiding significance. Therefore， optimizing the process conditions of Foshou yam and honey by the response surface methodology to obtain the optimal process parameters can effectively reduces the blindness of the test operation and provides a certain theoretical basis for actual production.
Conclusions and Discussion
This study investigated the effects of citric acid concentration， salt addition， pre-cooking time and honey concentration on the sensory quality of Foshou yam and honey can. Response surface analysis was used to optimize the best process conditions for Foshou yam and honey can. The optimal process conditions obtained after optimization were as follows： citric acid concentration 0.10%， salt addition amount 0.10%， cooking time 14.00 min， and honey concentration 26.00%. Under these conditions， the produced Foshou yam and honey can was rich in nutrition， tasted sweet and soft， and had a good flavor， and the soup was clear. It is of great significance to the development and utilization of Foshou yam and the research and development of canned health foods.
References
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[2] TAO YC. Wonderful vegetables： Wuxue Foshou yam[J]. Nongcun Baishitong， 2014（2）： 31， 73. （in Chinese）
[3] WANG SJ， LIU HY， GAO WY. Characterization of new starches separated from different Chinese yam （Dioscorea opposita Thunb.） cultivars[J]. Food Chemistry， 2006， 99（1）： 30-37.
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[7] ZHANG SW， XU JG， GU Z， et al. Study on processing technology of canned yam soup[J]. XianDai NongYe KeJi， 2018（23）： 233， 238. （in Chinese）
[8] YANG XL， LI YB， WANG CQ. Optimization of production process of shape stability for canned diced tomatoes by response surface methodology[J]. The Food Industry， 2014， 35（8）： 55-58. （in Chinese）
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[Methods] The Foshou yam produced from Wuxue was used as a raw material to prepare Foshou yam and honey nutritional can by combining Foshou yam with honey through screening， pre-cooking， filling， exhausting， cooling and other technical processes. The optimum technology parameter of Foshou yam and honey nutritional can was studied through single factor tests and response surface optimization.
[Results] The optimum technical parameters of Foshou yam and honey nutritional can were citric acid concentration 0.1%， amount of edible salt 0.1%， cooking time 14 min and honey concentration 26%. Under these conditions， the final sensory score was 90.20. The prepared can was not only rich in nutrition， but also had good flavor and taste.
[Conclusions] This study provides reference for the development and utilization of Foshou yam and the research and development of functional food.
Key words Foshou yam; Honey; Can; Single factor experiment; Response surface method
Received： August 12， 2020 Accepted： Ocotber 20， 2020
Supported by 2018 Undergraduate Innovation and Entrepreneurship Training Program of Huanggang Normal University （201810514045）; High-level Cultivation Project of Huanggang Normal University （201816703）.
Siying CHEN （1999-）， female， P. R. China， major： food science and engineering.
*Corresponding author. E-mail： 843076915@qq.com.
Foshou yam is a local national geographical indication product in Wuxue， which is rich in fiber and will produce a feeling of fullness after consumption. It has an antiobesity effect， and can be said to be a delicacy with the effects of prolonging life for consumers who are pursuing green and healthy[1-2]. Foshou yam is a famous Chinese medicinal material. The medical sage Li Shizhen proposed in Compendium of Materia Medica that it has the functions of treating various deficiency， treating exhaustion or lesion of the five internal organ and seven damages， removing wind in head， relieving low back pain， eliminating dysphoria with smothery sensation， and tonifying heat-qi[3]. Foshou yam has a very low soluble sugar content， and is rich in 17 kinds of amino acids and a variety of trace elements. It is high in nutrition and low in calories， and is a good food material for lowering blood sugar， lowering blood pressure， resisting tumor， and strengthening immunity. It is the king of yam for food supplements， and has the reputation of "Dabie Mountain Ginseng"[4]. Honey has many functions such as maintaining beauty and keeping young， resisting bacteria and inflammation， promoting digestion， improving sleep， protecting liver， moistening lungs and expelling phlegm to arrest coughing， clearing damp， promoting urination， calming the mind， clearing away heat and toxic materials， and relaxing bowel[5]. Wuxue Foshou yam is loved by more and more people because of its unique taste and nutritional value. However， due to the poor storage resistance of Foshou yam， it is prone to browning[6]， resulting in seasonality and short sales time. Taking into account the high nutritional value of Foshou yam and honey and few reports on the research of Foshou yam and honey can[7]， we prepared a kind of Foshou yam honey nutrition can using Foshou yam and honey as the main raw materials after screening， pre-cooking， filling and exhausting， cooling and other processes， determined the best values of citric acid concentration， salt addition， pre-cooking time and honey concentration through single factor test and response surface optimization[8]， and screened out the optimal process parameters for production of Foshou yam and honey can. This study improved the sensory quality of Foshou yam and honey can， which meets consumer’s demand and provides reference for the development and utilization of Foshou yam and the research and development of functional foods.
Materials and Methods
Materials and Instruments
Foshou yam， salt： commercially available; Guanshengyuan honey： Shanghai Guanshengyuan Bee Products Co.， Ltd.; citric acid （food grade）： Zhengzhou Cangyu Food Chemical Co.， Ltd.; calcium chloride （food grade）， sodium D-isoascorbate （food grade）： Henan Wanbang Industrial Co.， Ltd.
Peeling knives， cutting boards， knives， induction cookers， glass jars： commercially available; electronic balance （CP413）： Ohaus Instruments （Changzhou） Co.， Ltd.
Experimental methods
Foshou yam screening→peeling→cutting→color protection→pre-cooking→rinsing→canning→soup injection→exhausting→sealing→sterilization→cooling[6， 9， 10].
① Color protection： Since the peeled Foshou yam is prone to browning， the peeled Foshou yam was quickly put into a composite color protection solution prepared by citric acid 1.5 g， calcium chloride 0.5 g and D-sodium erythorbate 0.8 g to protect the color for 30 min， so as to prevent browning of Foshou yam.
② Pre-cooling and rinsing： The yam subjected to color protection was put into boiling water for pre-cooking until the yam was fully cooked， and the pre-cooked yam was quickly put into cool water to cool it， wash away the color protection solution on the surface of Foshou yam and further rinse off small pieces of yam.
③ Soup injection： The soup in this step was prepared by mixing citric acid， salt， honey and boiled pure water. ④ Sterilization and cooling： The boiling water temperature was heated to 100 ℃， and sterilization was performed for 5 min. Cooling meant to put the cans in cooling water to cool and then wipe off the water remaining on the surface of the cans， and finally put them in a refrigerator for 2-3 d.
Sensory evaluation standard of Foshou yam and honey nutritional can
The sensory evaluation method adopted a hundred-point system. 29 experts with sensory evaluation experience were selected to score the four items of color， shape， flavor， and taste of canned Foshou yam honey to select the best technological formula. The sensory evaluation standards are shown in Table 1[6，10].
Design of single factor tests
The effects of citric acid concentration， salt addition， pre-cooking time and honey concentration on the sensory quality of Foshou yam and honey can were to be explored. With other three factors set as fixed values， the citric acid concentration （0.06%， 0.08%， 0.10%， 0.12%， 0.14%）， salt addition （0.05%， 0.10%， 0.15%， 0.20%， 0.25%）， pre-cooking time （8， 10， 12， 14， 16 min） and honey concentration （20%， 22%， 24%， 26%， 28%） were changed for single factor experiments.
Response surface analysis
On the basis of single factor tests， the sensory evaluation score （Y） was used as the response value of the investigation， and the concentration of citric acid （A）， salt addition （B）， pre-cooking time （C）， and honey concentration （D） were used as the investigation factors. The Box-Behnken in Design-Expert software was used to design a four-factor three-level test， and the response surface methodology was used to optimize the best process parameters of Foshou yam and honey can.
Results and Analysis
Results and analysis of single factor tests
Effect of citric acid concentration on the sensory quality of Foshou yam and honey can
The effect of citric acid concentration on the sensory quality of Foshou yam and honey can is shown in Fig. 1. It can be seen from Fig. 1 that with the increase of citric acid concentration， the sensory score of Foshou yam and honey can showed a trend of first increasing and then decreasing. When the concentration of citric acid was 0.10%， the sensory score of Foshou yam and honey can was the highest. Meanwhile， the taste of the canned food was soft and glutinous， sour and sweet， and when the concentration of citric acid continued to increase， the sourness of Foshou yam and honey nutritional can increased and the sensory score decreased. It can be obtained that the optimal citric acid concentration was 0.10%， so 0.08%， 0.10% and 0.12% were selected as the three levels of citric acid concentration. Effect of salt addition on the sensory quality of Foshou yam and honey can
The effect of salt addition on the sensory quality of Foshou yam and honey can is shown in Fig. 2. It can be seen from Fig. 2 that as the amount of salt added increased， the sensory score first increased and then continued to decrease. When the amount of salt added was 0.10%， the sensory score reached the highest score. Adding too much salt reduced the sweetness of the can and made the flavor worse. It can be obtained that the optimal amount of salt was 0.10%， so 0.05%， 0.10% and 0.15% were selected as the 3 levels of salt added.
Effect of pre-cooling time on the sensory quality of Foshou yam and honey can
The effect of pre-cooking time of Foshou yam on the sensory quality of Foshou yam and honey can is shown in Fig. 3. It can be seen from Fig. 3 that with the increase of the pre-cooking time， the sensory score first continued to increase and then decreased. When the pre-cooking time was 14 min， the sensory score reached the highest， indicating that the sensory index of Foshou yam and honey can reached the best， and it was easy to be accepted. It can be concluded that the optimal pre-boiling time was 14 min， so 12， 14 and 16 min were selected as the 3 levels of the pre-cooking time of Foshou yam.
Effect of honey concentration on the sensory quality of Foshou yam and honey can
The effect of honey concentration on the sensory quality of Foshou yam and honey can is shown in Fig. 4. It can be seen from Fig. 4 that as the honey concentration increased， the sensory score first increased and then decreased. When the honey concentration increased to 26%， the sensory score reached the highest， which showed that the honey concentration of 26% was the sweetness easy to accept. It can be obtained that the optimal honey concentration was 26%， so 24%， 26% and 28% were selected as the 3 levels of honey concentration.
Results and analysis of response surface analysis test
Factor level selection
Combining the above single factor test results， with the sensory score of Foshou yam and honey can as the response value （Y） and citric acid concentration （A）， salt addition （B）， pre-cooking time （C）， and honey concentration （D） as factors， the Box-Behnken of the Design-Expert 8.0.6 software was used to design a four-factor three-level response surface optimization test， and a prediction model required for response surface test analysis was established. The factor levels are shown in Table 2[7]， the experimental design and results are shown in Table 3. Analysis of response surface test results
Data in Table 3 was subjected to analysis of variance to get a quadratic polynomial regression model： Sensory evaluation=+89.98-0.050A-0.075B+0.067C-0.33D-0.45AB-0.28AC-0.13AD+0.58BC-0.35BD+0.40CD-1.57A2-2.06B2-1.39C2-2.28D2. The regression analysis of variance is shown in Table 4.
The results of the variance analysis of the response surface regression model are shown in Table 4. From Table 4， we can see that： the model P<0.000 1 indicated that the response surface regression model reached an extremely significant level; P value of the lack of fit term was 0.895 7>0.05， which was not significant， indicating that the regression model could well fit the actual measured values; the correlation coefficient R2=0.959 1 indicated that the test error was small and the model fit well; and the adjusted correlation coefficient R2Adj=0.918 1 indicated that the model could explain 91.81% of the change in the response value， and the model could be used to predict and analyze the processing conditions of Foshou yam and honey can[7，11]. The F value can reflect the effects of various factors on test results， and the value of the F value was directly proportional to the effect[12-13]. It can be seen from Table 4 that the effects of the four factors on the sensory quality of Foshou yam and honey can be D （concentration of honey）>B （addition of salt）>C （pre-cooking time）>A （concentration of citric acid）. In the model， the one degree term D had a significant effect on the sensory evaluation of Foshou yam and honey can （P<0.05）， and other one degree terms had no significant effect; the interaction item BC had a significant effect （P<0.05）， and other interaction items had no significant impact; and the effects of the quadratic items A2， B2， C2 and D2 were all extremely significant （P<0.000 1）.
Response surface analysis of multi-factor interaction
Fig. 2 visually shows the response values and contour analysis diagrams of interaction between various factors. The flatter the edge of each factor in the figure， the smaller the effect of the factor on the sensory score， and the steeper the edge of the factor， the greater the effect of the factor on the sensory score[14]. Fig. 2（A） shows that when the pre-cooking time was 14 min and the honey concentration was 26%， the increase in citric acid concentration was smaller than that of salt， indicating that among the sensory effects on Foshou yam and honey can were in order of B>A. Fig. 2（B） shows that when the honey concentration was 26% and the salt addition was 0.10%， the citric acid concentration increased less than the pre-cooking time， indicating that the sensory effect on Foshou yam and honey can were in order of C>A. Fig. 2（C） shows that when the concentration of citric acid was 0.10% and the concentration of honey was 26%， the increase in pre-cooking time was smaller than the amount of salt added， indicating that the sensory effects on Foshou yam and honey can showed an order of B>C. Fig. 2（d） shows that when the pre-cooking time was 14 min and the citric acid concentration was 0.10%， the increase in salt addition was smaller than honey concentration， indicating that the sensory effects on Foshou yam and honey can were in order of D>B. Fig. 2（e） shows that when the concentration of citric acid was 0.10% and the amount of salt was 0.10%， the pre-cooking time increased less than the honey concentration， indicating that the sensory effects on Foshou yam and honey can exhibited an order of D>C. Fig. 2（f） shows that when the salt addition was 0.10% and the pre-cooking time was 14 min， the increase in citric acid concentration was smaller than that of honey， indicating that the sensory effects on Foshou yam and honey can were in order of D>A. Verification results
Through the prediction of the regression model， under the parameters of citric acid concentration 0.10%， salt addition 0.10%， pre-cooking time 14.03 min， and honey concentration 25.86%， the sensory evaluation score of Foshou yam and honey can was the highest. In consideration of the operability of the experiment， the process parameters were adjusted to citric acid concentration 0.10%， salt addition 0.10%， pre-cooking time 14.00 min， and honey concentration 26.00% in the actual experiment. On this basis， three sets of parallel verification experiments were carried out， and finally， the sensory score of Foshou yam and honey can was 90.20±0.58， which was close to the predicted value， indicating that the model was reliable and had certain practical guiding significance. Therefore， optimizing the process conditions of Foshou yam and honey by the response surface methodology to obtain the optimal process parameters can effectively reduces the blindness of the test operation and provides a certain theoretical basis for actual production.
Conclusions and Discussion
This study investigated the effects of citric acid concentration， salt addition， pre-cooking time and honey concentration on the sensory quality of Foshou yam and honey can. Response surface analysis was used to optimize the best process conditions for Foshou yam and honey can. The optimal process conditions obtained after optimization were as follows： citric acid concentration 0.10%， salt addition amount 0.10%， cooking time 14.00 min， and honey concentration 26.00%. Under these conditions， the produced Foshou yam and honey can was rich in nutrition， tasted sweet and soft， and had a good flavor， and the soup was clear. It is of great significance to the development and utilization of Foshou yam and the research and development of canned health foods.
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