6 MASS. EXPERIMENT STATION BULLETIN 408 



Determination of pH Value 



The pH value of the different foods was determined by means of a Beckman 

 pH meter, using glass and calomel electrodes. 



Relative Quality 



The grade of eggs was determined by candling. Their relative quality was 

 measured by comparing their odor, loss in weight, and increase in air cell size and 

 by an examination of the egg albumin for appearance and texture. 



The relative quality of fruits and vegetables was evaluated by organoleptic 

 observations, ascorbic acid (vitamin C) content, and bacteria counts. The 

 organoleptic tests included a comparison of odor, flavor, texture, surface dis- 

 coloration and drying, and general appearance. 



The bacteriological condition of the foods studied was determined by means of 

 plate counts as described by Geer, Murray and Smith (1933). 



The ascorbic acid content of the samples was determined whenever possible, 

 because vitamin C is considered to be a good index of quality of fruits and veg- 

 etables. Their vitamin C content closely parallels their quality as regards variety, 

 overmaturity, length of time in storage, and overcooking. 



In this investigation the ascorbic acid content of the test foods was determined 

 by the 2,6-dichlorophenolindophenol dye titration method of Tillmans, Hirsch 

 and Hirsch (1932) as described by Maclinn and Fellers (1938). The dye solution 

 was standardized according to the method of Buck and Ritchie (1938). The 

 vitamin C content was calculated as milligrams of ascorbic acid per 100 grams 

 on a moist basis or, in cases where dehydration occurred, it was calculated as 

 milligrams per one gram of dry matter. 



OPERATING CONDITIONS 



The refrigerators were adjusted so that they maintained a cabinet temperature 

 within 1°F. of each other. Different conditions with regard to door openings 

 and food load were set up in order to determine their effect on the operation of 

 the refrigerators. 



The temperature and relative humidity of the refrigerators were determined 

 when the cabinets were empty and again when they contained a normal food 

 load, consisting of representative foods and jars of water. A tray of ice cubes 

 was frozen each day and articles of food were replaced by others at room tempera- 

 ture in order to simulate conditions in a typical household. An average of twenty- 

 five door openings per day was made in both of these tests, for it had been found 

 that household refrigerators are opened about twenty-five times a day. 



The daily power consumption during these tests was calculated from the 

 kilowatt hour and running time readings obtained as described above. 



Effect of Food Load on Temperature and Relative Humidity 



There was no noticeable effect on the average temperature within the cabinets 

 caused by different food loads. However, as was to be expected, when quantities 

 of hot foods were placed in the cabinets a temporary rise in temperature was 

 observed. 



The effect of food load and door openings on the relative humidity of the 

 cabinets is presented in Table L An average-sized food load caused an increase 

 of 10-15 percent in the relative humidity. 



