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I Marketing Research Report No. 598 



NATfOr"' *~? 



U. S. DEPT. OF AGRICULTURE 
~" M ' 'IBRARY 

WAY I 6 1963 



Effects of 



JWOISTURE CONTENT, HUMIDITY, 
AND LENGTH OF STORAGE 



on Maintenance of Quality in 

ROUGH RICE 



UNITED STATES DEPARTMENT OF AGRICULTURE 

Agricultural Marketing Service, Market Quality Research Division 

and 

Agricultural Research Service, Crops Research Division 



PREFACE 

This report is based on a laboratory study of three factors 
and their interactions that affect the maintenance of quality of 
rough rice during storage. It is part of a broad study of the cause 
and control of microbiological, chemical, and physical deteriora- 
tion of rough rice in relation to off -farm conditioning, handling, 
and storage in the south central States. 

The research was conducted in cooperation with the Crops 
Research Division, Agricultural Research Service; the Depart- 
ment of Plant Sciences, Texas Agricultural Experiment Station; 
and the Rice-Pasture Experiment Station, Beaumont, Tex. 



CONTENTS 

Page 

Summary 3 

Introduction , 3 

Methods 3 

Experimental results 5 

Moisture content of the rice during storage 5 

Mold development 5 

Germination 6 

Milling yields 6 

Color of milled rice 6 

Damaged and heat-damaged kernels 6 

Odor of milled rice 6 

Factors related to cooking behavior 6 

Discussion 7 

Literature cited 8 

Tables 10 









Washington, D.C. April 1963 



EFFECTS OF MOISTURE CONTENT, HUMIDITY, AND LENGTH OF STORAGE 
ON MAINTENANCE OF QUALITY IN ROUGH RICE 

By Harry W. Schroede replant pathologist, Market Quality Research 
Division, Agricultural Marketing Service: and John V.'-Halick, 
formerly biochemist, Crops Research Division, Agricultural Re- 
search Service. 

SUMMARY 

Two series of samples of rough rice (one at 13.4 percent moisture and the other at 
23.6 percent) were stored in relative humidities ranging from 62 to 100 percent. The 
prevalence of molds and the quality characteristics of the rice were determined after 45, 
87, and 186 days' storage. 

Analyses of the counts of total, field, and storage molds showed that initial moisture 
content, relative humidity of storage, time in storage, and all their interactions were 
highly significant sources of variance. The data further indicated that the composition of 
the mold flora of stored rice is extremely variable and may change rapidly under varying 
storage conditions. 

A high level of metabolic activity of the total mold flora, rather than of a specific 
group of fungi, appeared to be associated with deterioration of the stored rice. Deteriora- 
tion was evidenced to a greater degree by color, kernel discoloration, and odor than by 
changes in cooking characteristics. 

INTRODUCTION 

The association of molds with deterioration of stored grains has been studied by 
many investigators in recent years. Christensen (J) 1 has published a comprehensive re- 
view of this work. The emphasis in past studies has been primarily upon investigation of 
the effects of moisture content and temperature on mold development and the related de- 
terioration of stored grain. 

The present study was made to determine the effect of initial moisture content, rel- 
ative humidity of storage, time in storage, and the interaction among these factors on 
type and prevalence of molds and on the associated deterioration of rough rice. 

The relation of deterioration during storage to the cooking behavior of the milled 
grain also was studied, since, to the authors' knowledge, little or no information on this 
relationship is available. 

METHODS 

An early-maturing long-grain rice, an experimental selection grown at the Rice- 
Pasture Experiment Station, Beaumont, Tex. , was harvested late in July at a moisture 
content of 24 to 25 percent 2 and transported immediately to College Station, Tex. It was 
stored in sealed containers and refrigerated at 45° F. for about 30 days. 



Underlined numbers in parentheses refer to items in Literature Cited, p. 8. 

Percent moisture of rice samples in this paper is given on the "wet basis"; that is, the percent moisture represents 
the amount of water by weight in a sample divided by the total weight of the sample (dry matter plus water). 



Approximately 28 pounds of the rice was mixed thoroughly, then divided into two equal 
parts with a Boerner sampler . One part was dried at room temperature to 13.4 percent 
moisture content, on screen trays. The moisture content of the other portion was 23.6 
percent. Each of the two sublots was divided into 20 samples. 

Five samples from each sublot were reserved as controls. The control samples 
were individually dried at room temperature to a satisfactory moisture content (12 per- 
cent) for milling purposes. Three aliquants of 100 kernels from each control sample 
were then plated on malt-salt (7. 5 NaCl) agar for moid-content determinations. Of each 
control, 125 grams was milled, the milling yields and damaged kernels were determined, 
and the head rice (whole kernels after milling) retained for quality comparisons later 
with the stored samples. Sufficient unmilled grain also was retained to make seed viabil- 
ity tests of all samples at the end of the storage period. All samples were milled with a 
modified McGill portable mill. They were milled under 15 pounds pressure for 30 sec- 
onds, then polished for 30 seconds under 5 pounds pressure. The broken kernels were 
removed with the USDA rice -sizing device. 

Mold counts were made as described by Schroeder and Sorenson (8), an adaptation 
of techniques described by Christensen (3). In the present paper, the term "mold preva- 
lence" refers to the percent of seeds from which a mold or molds were isolated. Molds 
were classified as field or storage molds according to Christensen (3). The field molds 
are those species which primarily infest the kernels before harvest. Some field molds 
have been associated with discolored kernels by Tullis (12). The storage molds, post- 
harvest invaders, are primarily species of the genera Penicillium and Aspergillus . 
Yeasts and bacteria also may have been active in those samples stored at high relative 
humidities (!_1); however, the malt-salt agar medium used in this experiment is not fa- 
vorable for isolating these organisms, so their relative prevalence was not determined. 

Fifteen samples from each sublot were stored in cylindrical copper-screen baskets 
suspended in quart Mason jars over saturated salt solutions (table 1). Salt solutions 
were selected, from the International Critical Tables (9), that would maintain paired 
samples of the initially 13.4- and 23.6-percent rice at approximately the same moisture 
content after the rice came to equilibrium with the storage atmosphere within the jars. 
The equilibrium moisture contents were calculated from the data reported by Breese Q), 
allowing for the hysteresis effect of adsorption and desorption. The jars were stored in 
the laboratory, where the temperature varied from 70° to 80° F. The mean temperature, 
estimated from thermograph charts, was about 72° F. during the first 3 months of stor- 
age and about 75° F. for the remainder of the storage period. 

Thus, three sets of five paired samples, excluding the controls, constituted the ex- 
perimental design. In each pair, the samples were expected to reach approximately the 
same moisture content when equilibrium with the storage atmosphere was reached; one 
sample by adsorption, the other by desorption. The time required for rice to equilibrate 
with the atmosphere under these conditions is not known, but on the basis of the findings 
by Breese (1_), the samples were expected to approach equilibrium moisture content 
within 3 to 5 days. 

One set of samples was removed from storage after 45, 87, and 186 days, respec- 
tively. The moisture content was determined on aliquants of each sample by the two-stage 
air-oven method. The remainder of each sample was air-dried at room temperature to 
approximately 12. 5-percent moisture content. The samples were then evaluated, follow- 
ing the procedure described for the control samples. 



3 Use of trade names in this report is for identification only, and does not constitute endorsement of the product named 
or imply discrimination against other products. 

- 4 - 



Measurement of quality characteristics related to cooking behavior included deter- 
mination of birefringence end-point temperatures (BEPT) 4 , by the method of Pfahler et 
al . (7), on a composite sample of 10 kernels. The amylose contents of the samples were 
determined by the method of Williams et al. (L3) as modified by Hogan et al. (6). The re- 
lation of BEPT and gelatinization characteristics to cooking behavior has been established 
previously (4), as has the value of amylose content as an index of cooking behavior 
(5, L3). A small portion of each sample was also boiled under prescribed conditions (5), 
soaked in distilled water overnight, and examined for broken, odd-shaped, split, and 
ragged grains. Each sample was rated numerically from 1 to 7 (good to poor) on its 
overall appearance. Reducing and nonreducing sugars were determined according to the 
procedure outlined by the American Association of Cereal Chemists (10). 

EXPERIMENTAL RESULTS 

Moisture content of the rice during storage. --The actual moisture contents of the 
rice samples stored in atmospheres with relative humidities controlled by saturated salt 
solutions did not agree with those postulated (table 1, page 10). These differences may be 
partly varietal, since Breese (1), on whose work the calculations were based, used a 
different rice variety. More probably the differences were caused by the activities of the 
microbial flora, either directly or through changes in the composition of the rice caused 
by their metabolic activities. 

Mold development. --The three factors (prestorage moisture content, relative humid- 
ities during storage, and days in storage) and their interactions were found to have a 
highly significant effect on mold flora, exceeding the 1-percent probability level (table 2). 
This was true for all mold classifications except Penicillium spp. , which was not signifi- 
cantly affected by the prestorage moisture content or the interaction of this factor with 
relative humidities or days. However, the three-factor interaction was highly significant, 
as was the interaction of relative humidities with days in storage. 

Field molds decreased as storage molds increased. After 187 days, storage molds 
were dominant in all treatments except in rice having 23. 6 percent moisture initially 
stored at the lowest relative humidity. In general, the incidence of field molds was 
greater in the initially 23.6-percent moisture rice at all relative humidities than in 13.4- 
percent moisture rice (table 3). 

One notable result was the almost total elimination of viable molds in 45 days from 
13.4-percent rice stored at a relative humidity of 93 percent (table 3). No reasonable ex- 
planation of this phenomenon is apparent in these data. 

Penicillium spp . were not significantly affected by the initial moisture content of the 
rice. They comprised a minor portion of the flora of all samples except those stored in 
atmospheres having a high relative humidity. However, a trend toward increasing preva- 
lence of this genus was apparent as time in storage and the moisture content of the rice 
increased (table 4). 

Considering the entire experiment, the Aspergillus glaucus and the A. candidus 
groups were almost equally prevalent. A_. glaucus spp. were isolated from an average of 
16. 8 percent of the kernels, compared to 16. 7 percent for A. candidus . The A_. glaucus 
group was most prevalent in the initially low-moisture rice, while the A. candidus group 
tended to be associated with the initially high-moisture rice. The prevalence of species of 
the A_. flavus-oryzae group was relatively low under the conditions of this experiment 
(table 5). 



* When viewed under polarized light, rice starch granules appear brilliantly illuminated with the exception of two dark lines 
which intersect at the hilum. This phenomenon is known as birefringence. The temperature at which the loss of birefrin- 
gence occurs is termed the birefringence end-point temperature, or simply, BEPT. There is a very high positive correlation 
between the BEPT of a sample and its gelatinization temperature as determined with an amylograph. 



Germination . --The initially high-moisture rice did not germinate as well as the 
low-moisture rice, regardless of the humidity and duration of storage. Germination of 
rice of both initial moisture contents decreased with increasing relative humidities of 
storage. Treatment D resulted in 0-percent germination in 45 days' storage of the high- 
moisture rice and in 87 days' storage of the low-moisture rice. With treatment E, 15 
percent of the kernels of the low-moisture rice germinated after 186 days' storage, 
compared with 0-percent germination for the high-moisture rice. 

Milling yields. --Treatments A, B, C, and D did not materially affect milling yields 
during the entire storage period. Samples of the low- and high-moisture sublots were 
milled at the beginning of the experiment, and the low-moisture rice yielded 69 percent 
total and 33 percent head rice, compared to 66 and 30 percent for the high-moisture rice. 
After 186 days' storage, the final averages of the milling yields for treatments A through 
D were 67 and 33 percent and 65 and 34 percent, respectively. 

Yields of milled rice from the samples stored over water (treatment E) were ex- 
tremely low after 186 days' storage. The initially low-moisture rice milled 25-percent 
total rice and 0-percent head rice, and the initially high-moisture rice milled 35 and 5 
percent. 

Color of milled rice . --All treatments except A, B, and C of the initially low-mois- 
ture rice caused undesirable color changes by the end of the storage period (table 6). 

Damaged and heat-damaged kernels . --These terms are applied to discolored kernels 
and are factors in determining the official U. S. grades. Kernels classified as heat- 
damaged are dark amber, while those classed as damaged are less severely discolored. 
The number of damaged and heat-damaged kernels was greatest in the high-moisture rice 
in all treatments. It increased as the relative humidity and the time in storage increased 
(table 6). 

Odor of the milled rice . --The milled rice did not have an undesirable odor until it 
had severely deteriorated. Initially low-moisture rice in treatments A, B, and C did not 
develop an undesirable odor during the entire storage period, but all treatments of the 
high-moisture rice resulted in milled rice with a musty odor prior to or after 186 days' 
storage. Some samples from both initial moisture -content rice sublots smelled musty as 
rough rice but had no undesirable odor after milling (table 6). 

Factors related to cooking behavior . --The effects of the treatments and storage time 
on the cooking characteristics of the rice are summarized in table 7. Except for bire- 
fringence end-point temperature (BEPT) determinations, the samples were so small that 
replication was not possible. Analysis of the BEPT determinations showed that relative 
humidity of storage ("treatment" in table 7), storage time, and all interactions were 
highly significant sources of variance. The initial moisture content of the rice was sig- 
nificant only at the 5-percent level. After 45 days' storage, the BEPT's of the samples 
showed a slight increase, particularly in high-moisture rice. However, with increasing 
storage, this trend appeared to be reversed, and after 186 days' storage, the BEPT's of 
samples from both moisture levels were consistently lower than at the beginning of the 
test. 

The amylose content of the rice samples remained relatively constant for the first 87 
days' storage, but at the end of 186 days, a slight increase was noted. 

Reducing and nonreducing sugars have long been considered a good index of deteriora- 
tion in cereals (2, M). However, the largest increase in sugar content was associated 
with loss of viability of the rice. With 45 and 87 days' storage, the sugar content was 
highest for treatment D but somewhat lower for treatment E. 



DISCUSSION 

Many factors affect deterioration and mold development in rough rice. Three of 
these factors were studied and their effects are separated here. They are: (1) Moisture 
content of the rice when stored; (2) relative humidity of the storage atmosphere; and (3) 
length of the storage period. The effect of all other factors was minimized by conducting 
the experiment with a small homogeneous lot of rice and by keeping all sample storage 
chambers in the same environment. 

Analyses of variance of the mold counts indicated the complexity of the effect of the 
three factors. These factors and their interactions were all highly significant sources of 
variation in the relative prevalence of all molds, field molds, and storage molds (table 
2). The percent of kernels with molds in the initially low-moisture rice was lower as 
storage humidity was decreased and time in storage was increased. With the initially 
high-moisture rice, treatment D (rice stored over a saturated solution of NH4H2PO4.) 
mold counts failed to follow the pattern of relationship with relative humidity and time in 
storage that was evident in the remainder of the experiment. Volatiles from the salt solu- 
tion may have had an inhibitory or toxic effect on certain species of molds, primarily 
the field molds (table 3). 

Increased competition by storage molds, favored by storage atmospheres of low 
relative humidity, was associated with the decrease in isolatable field molds. Relative 
humidity of storage interacted significantly with the initial moisture content of the rice. 
For example, in treatment A, after 186 days' storage, field molds were isolated from 
30.6 percent and storage molds from 40.6 percent of the initially low-moisture rice, 
compared to 93. 6 and 20. 3 percent of the high-moisture rice. The increase in storage 
molds was affected primarily by storage humidity and the length of the storage period 
(table 3). Therefore, it is concluded that the specific composition of the mold flora of 
stored rice is a result of the storage environment and the competitive ability of the molds 
in the grain at any given time. Similar results were obtained in larger lots of rice in 
aerated storage by Schroeder and Sorenson (j3) . 

Stored rice will seldom be exposed to environmental conditions similar to the more 
extreme conditions in the present experiment; that is, extended storage of high-moisture 
rice in a highly humid atmosphere. In a normal storage environment, approximated by 
treatments A and B, these data show that storage molds are the best competitors and can 
be presumed to be physiologically more active than the field molds. 

The effect of the third factor (time in storage) is illustrated by comparing total mold 
isolations with the comparable data for field and storage molds (table 3). With initially 
low-moisture rice, a gradual decrease in total molds as time in storage increased was 
apparent in treatments A and B. The field molds were dying at a faster rate than the 
storage molds were infesting the rice. However, total mold counts could be expected to 
approach maximum prevalence, a reversal of the indicated trend, if the storage period 
was extended. These data also clearly show the effect of the interaction between time in 
storage and the two other factors studied. 

In the present experiment, species of the genus Aspergillus were more numerous 
than species of Penicillium (table 3). According to Christensen (3), this is generally true 
in all stored grains. The _A. glaucus group predominated in the initially low-moisture 
rice, while the A. candidus group was predominant in the high-moisture rice (table 4). 
However, the relative prevalence of these specific groups could easily be influenced by 
uncontrolled factors such as the amount of inoculum (spores, etc.) in the rice at the be- 
ginning of the experiment. Although a small quantity of well-mixed rice (presumed homo- 
geneous) was used, the preparatory steps preceding storage could have introduced such a 
factor. 

Deterioration, on the basis of factors affecting the U. S. grade of the rice, proceeded 
at an accelerated rate as time in storage, the relative humidity of the storage, and the 

- 7 - 



initial moisture content of the rice increased (table 6). However, these data do not show 
a clear relationship between the grading factors and the relative prevalence of field 
molds versus storage molds. 

The effect of the storage treatments and mold development on the cooking character- 
istics of the rice was not clearly defined by these data. Although the overall appearance 
of the cooked grains of the experimental selection used in this study was not desirable, 
it was not greatly altered by the mold growth associated with the various treatments. All 
samples of the initially low-moisture rice were white after cooking. Even severely dis- 
colored rice from the initially high-moisture samples was much lighter in color after 
cooking. 

The birefringence end-point temperature is related to the time required to cook a 
sample. However, except in samples having extreme BEPT's, the small differences 
noted here, though significant, would probably not result in much practical difference in 
cooking time. 

This study shows that the mold flora of rough rice comprises a large and varied 
group of fungi. It shows that molds are closely associated with deterioration of rice in 
storage. The multiplicity of factors affecting mold activity in stored rice, all of which 
appear to interact significantly with each other, increases the difficulties in reaching an 
adequate solution to the problem. Basic knowledge can and should be obtained by a sys- 
tematic study of specific molds. Those species of little practical importance could then 
be disregarded and the effects of environmental factors on infestation and growth of 
those molds primarily associated with deterioration could be determined. 

LITERATURE CITED 

1. Breese, Michael H. Hysteresis in the Hygroscopic Equilibria of Rough Rice at 25° 

C. Cereal Chem. 32: No. 6. 1955. 

2. Bottomley, R. H. , Christensen, C. H. , and Geddes, W. F. Grain Storage Studies 

IX. The Influence of Various Temperatures, Humidities, and Oxygen Concen- 
trations on Mold Growth and Biochemical Changes in Stored Yellow Corn. Ce- 
real Chem. 27:271-296. 1950. 

3. Christensen, C. M. Deterioration of Stored Grains by Fungi. Bot. Rev. 23:108-134. 

1957. 

4. Halick, J. V. , and Kelly, V. J. Gelatinization and Pasting Characteristics of Rice 

Varieties as Related to Cooking Behavior. Cereal Chem. 36:91-98. 1959. 

5. Halick, J. V. , and Keneaster, K. K. The Use of a Starch-Iodine -Blue Test as a 

Quality Indicator of White Milled Rice. Cereal Chem. 33:315-319. 1956. 

6. Hogan, J. T. , Hawley, P. S. , and Deobald, H. J. Note on the Determination of 

Amylose Content of Rice. Cereal Chem. In press. 

7. Pfahler, P. L. , Kramer, H. H. , and Whistler, R. L. Effect of Genes on Birefrin- 

gence End-Point Temperatures of Starch Grains in Maize. Science 125:441-442. 
1957. 

8. Schroeder, Harry W. , and Sorenson, J. W. , Jr. Molds in Rough Rice Aerated in 

Storage. Rice Jour. 64:6, 8-10, 12, 21-23. 1961. 

9. Spencer, Hugh M. Laboratory Methods for Maintaining Constant Humidity. Interna- 

tional Critical Tables. Vol. 1:67. 



8 - 



10. Swanson, E. C. Cereal Laboratory Methods. P. 87. American Association of 

Cereal Chemists, St. Paul, Minn. 1957. 

11. Teunisson, Dorothea J. Influence of Storage Without Aeration on the Microbial 

Populations of Rough Rice. Cereal Chem. 31:462-474. 1954. 

12. Tullis, E. C. Fungi Isolated from Discolored Rice Kernels. U.S. Dept. Agr. 

Tech. Bull. 540. 1936. 

13. Williams, Virginia R. , Wu, W. T. , Tsai, H. Y. , and Bates, H. G. Varietal Dif- 

ferences in the Amylose Content of Rice Starch. J. Agr. Food Chem. 6:47-48. 
1958. 

14. Zeleny, L. , and Coleman, D. A. Acidity in Cereals and Cereal Products, Its De- 

termination and Significance. Cereal Chem. 15:580-595. 1938. 



- 9 



TABLE 1. --Moisture contents of rough rice samples stored at various relative humidities 

maintained with saturated salt solutions 





Prestorage moisture 




Moisture content 












content and storage 
treatment 1 




Expected 


Actual after indie; 


ited days 




45 


87 


186 






Percent rela- 










13.4- percent: 


Salt tive humidity 2 
NaN0 3 75 


Percent 
12.6 


Percent 
14.2 


Percent 
13.6 


Percent 


A 


13.6 


B 


(NH4) 2 S0 4 


81 


13.9 


14.9 


14.5 


14.3 


C 


KC1 


85 


15.1 


16.0 


15.0 


15.1 


D 


NH4H2PO4 


93 


17.7 


16.5 


15.7 


16.0 


E 


None 


100 


- 


20.4 


21.5 


22.7 


23.6 percent: 














A 


NH4NO3 


62 


12.4 


14.7 


13.0 


12.6 


B 


NaN0 3 


75 


14.0 


16.1 


14.4 


14.3 


C 


(NH 4 ) 2 S0 4 


81 


15.0 


17.7 


15.4 


15.3 


D 


NH4H2PO4 


93 


17.7 


20.5 


17.3 


16.4 


E 


None 


100 


- 


25.0 


25.5 


23.3 



The alphabetically designated treatments identify paired samples expected to reach 
approximately equal moisture contents when at equilibrium with the storage atmosphere. 
2 At 75° F. 



10 



TABLE 2. — Analyses of variance of mold determinations on rough rice showing the 
significance of main factors and interactions 



Source of 
variation 



D.F. 



F value for indicated molds 



Total 



Field 



Storage 



Pen. 



Total 

Moisture levels 
Replications. . . 
Days in storage 

Treatments 

ML X D 

ML X T 

D X T 

ML X D X T 

Error 



19 

1 


**117.69 


2 


.73 


3 


**59.12 


4 


**82 . 69 


3 


**31.85 


4 


**23.35 


12 


**30.54 


12 


**39.65 


78 





**334.8l 

2.66 

**712.36 

**203.14 

**41.95 

**16.76 

**35.36 

**30.50 



**22.58 

.58 

**543 . 24 

**99.09 

**13 • 67 

-**6.82 

**30.13 

**3.09 



.82 

1.09 
**93.45 
**47.18 

1. 

1. 



.95 
,68 



**42.91 
**3.86 



Source of 
variation 



D.F. 



F value for indicated molds 



Asp . 



A. 

Fl.-ory . 



A. 
Glaucus 



A. 
Candidus 



Total 

Moisture levels, 
Replications. . . , 
Days in storage , 

Treatments , 

ML X D , 

ML X T 

D X T , 

ML X D X T 

Error , 



19 
1 


**37.96 


2 


.35 


3 


**534.45 


4 


**92.16 


3 


**13 . 75 


4 


**10.53 


12 


**32.69 


12 


**3.39 


78 





*-*11.31 

.23 

**6.46 

*-*8.08 

**7.46 
**10.77 
**11.85 

**9.15 



**199. 88 

2.27 

**203 . 27 

**62.75 

**47.04 

**6.69 

**21.10 

**5.29 



**15.46 
2.36 
**227.08 
**34.10 
**10.46 
**28.95 
*-*17.44 
**10.87 



^^Significant at the 1-percent level. 



11 - 



TABLE 3. --Molds isolated after surface sterilization, from rough rice stored at 
different relative humidities for various periods 



Standard error of 
mean difference 





Prestorage moisture content of rice 


Storage period 
and treatment 1 


13.4 percent 


23.6 percent 
















Total 


Field 


Storage 


Total 


Field 


Storage 




molds 


molds 


molds 


molds 


molds 


molds 






Percent of kernels with molds 2 






Percent 


Percent 


Percent 


Percent 


Percent 


Percent 


days 3 


99.1 


98.5 


2.4 


99.1 


98.1 


2.2 


45 days : 














A 


91.0 


84.0 


20.0 


100.0 


99.0 


13.6 


B 


92.0 


90.6 


4.6 


100.0 


99.6 


15.3 


C 


96.0 


93.0 


11.3 


100.0 


98.6 


11.0 


D 


1.6 


1.6 


0.0 


99.6 


99.3 


2.0 


E 


99.3 


80.3 


64.6 


98.6 


82.0 


55.3 


87 days: 














A 


73.3 


62.0 


17.6 


98.6 


95.6 


12.3 


B 


78.0 


61.0 


28.6 


100.0 


98.6 


29.6 


C 


88.3 


40.3 


63.6 


98.6 


94.0 


19.0 


D 


62.0 


1.3 


61.3 


43.3 


4.0 


40.0 


E 


98.6 


29.6 


92.0 


79.3 


32.3 


56.0 


186 days : 














A 


67.0 


30.6 


40.6 


99.0 


93.6 


20.3 


B 


73.0 


10.3 


68.0 


100.0 


68.0 


81.6 


C 


90.3 


7.6 


86.6 


99.0 


56.3 


81.3 


D 


95.0 


0.0 


91.6 


92.0 


0.6 


91.3 


E 


100.0 


2.0 


99.6 


99.3 


7.6 


93.6 



+7.21 



+9.16 



+10.49 



+7.21 



+9.16 



+10.49 



1 The range of relative humidities of storage from A (62-75 percent) through E 
(100 percent) . 



Given as mean of 3 determinations except as noted below. 
3 Mean of 5 samples, 3 determinations each. 



- 12 - 



TABLE 4.- -A comparison of the prevalence of Penicillium and Aspergillus spp . isolated 
from rough rice kernels stored at different relative humidities for various periods 



Treatment and storage 
period 1 



Prestorage moisture content of rice 



13.4 percent 23.6 percent 



Penicillium spp. 



13.4 percent 23.6 percent 



Aspergillus spp. 



Prestorage check: 3 
days , 

A: 

45 days , 

87 " , 

186 " , 

B: 

45 days , 

87 " , 

186 " , 

C: 

45 days 

87 " , 

186 " 

D: 

45 days 

87 " , 

186 " 

E: 

45 days 

87 " 

186 " 

Standard error of 
mean difference 



Percent 



2.1 



7.3 
5.6 
2.6 



4.3 

5.0 
3.0 



2.0 
7.3 
0.6 



0.0 

1.0 

61.6 



7.6 
32.0 
35.3 



Percent 



1.9 



4.3 
4.6 
2.0 



4.6 

9.3 
7.0 



6.0 
2.0 
6.3 



0.0 

4.3 

48.0 



10.6 

9.0 

41.6 



Percent 



0.4 



Percent 



0.6 



15.6 


9.6 


12.3 


8.0 


39.3 


18.6 


0.3 


11.3 


25.0 


26.3 


66.3 


79.3 


9.6 


5.6 


58.3 


17.0 


86.6 


79.0 


0.0 


2.0 


60.6 


37.3 


90.6 


86.0 


62.0 


52.0 


89.0 


52.6 


93.6 


62.6 



+6.63 



+10.10 



1 The range of the relative humidity of storage from A (62-75 percent) through E 
(100 percent) . 

2 Given as the mean of 3 determinations as percent of surface -sterilized kernels from 
which molds were isolated, except as noted below. 

3 Mean of 5 samples, 3 determinations each. 



13 



TABLE 5.-- A comparison of the prevalence of the 3 most numerous groups of Aspergillus spp . 
isolated from rough rice kernels held at different relative humidities for various 
periods 



Treatment and storage 
period 1 



Prestorage moisture content of rice 



13.4 
percent 



23.6 
percent 



A. flavus-oryzae' 



13.4 
percent 



23.6 
percent 



A. glaucus 2 



13.4 
percent 



23.6 
percent 



A. candidus 2 



Prestorage check: 
days 



45 days. 
87 " . 
186 " . 



45 days. 
87 " . 
186 " . 



45 days. 

87 " . 

186 " . 



D: 



45 days. 
87 " . 
186 " . 



E: 



45 days. 
87 " • 
186 " . 



Percent Percent 



0.4 



0.6 
5.6 
1.0 



0.0 
0.3 
4.3 



0.0 
0.0 
3.0 



0.0 
0.0 
3.3 



1.0 
0.0 
1.0 



0.6 



0.0 
0.0 
0.0 



0.3 

4.3 

15.0 



0.0 
0.3 
0.6 



0.0 
0.0 
1.3 



39.0 
0.6 
1.6 



Percent Percent 



0.0 



0.3 

3.6 

23.3 



0.3 
22.0 
50.6 



4.0 
45.6 
50.0 



0.0 
56.6 

88.0 



27.0 
82.3 
59.3 



0.0 



0.3 
1.6 
1.3 



0.3 
3.0 
2.6 



0.0 
1.6 
4.3 



0.0 
14.6 
53.6 



0.6 

31.3 
38.0 



Percent Percent 



0.0 



14.6 

3.3 

17.0 



0.0 

4.6 

22.3 



6.0 
23.0 
54.3 



0.0 
5.6 
5.3 



40.6 
22.0 
69.3 



0.0 



9.3 

6.3 

11.0 



11.0 
23.0 
71.0 



5.6 
15.3 
76.6 



2.0 
23.3 
43.3 



20.3 
24.0 
26.6 



Standard error of mean 
difference 



+5.10 



+ 9.80 



+8.82 



1 The range of the relative humidity of storage from A (62-75 percent) through E (100 
percent) . 

2 Given as the mean of 3 determinations of percent of surface- sterilized kernels from 
which molds were isolated, except as noted .below. 

3 Mean of 5 samples, 3 determinations each. 



14 



TABLE 6. — Summary of the physical characteristics of the head rice milled from samples of 
rough rice stored at different relative humidities for various periods 



Treatment and storage 
period 1 



Color" 



Odor 



Damage 



Heat damage 



13.4$ prestorage moisture 
content : 

Prestorage check: 3 
days 



A: 



45 days. 
87 " . 
186 " . 



45 days. 
87 " . 
186 " . 



45 days. 
87 " . 
186 " . 



: : 



45 days. 
87 " . 
186 " . 



45 days. 
87 " . 
186 " 5 



23.6 prestorage moisture 
content : 

Prestorage check: 3 
days 



45 days. 
87 " . 
186 " . 



45 days. 
87 " . 
186 " . 



3: 



45 days. 
87 " . 
186 " . 



45 days. 
87 " . 
186 " . 



45 days. 
87 " . 
186 " . 



White 



White 



White 
Cream 
White 



White 



Cream 

Rosy 

Dark cream 



Cream 
Dark cream 



White 



Good 

Good 
it 
it 

Good 
ii 
ii 

Good 
ii 

ii 

Good 
ii 

Musty 

Good 4 
Musty 



Good 



White 
ti 


Good 4 


Light cream 


Musty 


Cream 

Gray 

Cream 


Good 4 
Musty 
ii 


Cream 
Gray to amber 
Cream 


Good 4 
Musty 
ii 


Amber 
ii 

Yellow brown 


Good 4 
Musty 
n 


Gray to amber 
it ti it 

Dark brown 


Good 4 
Musty 
ii 





1 kernel 





2 kernels 
8 " 
1 " 



2 kernels 
7 " 

7 



10 kernels 
8 percent 



11 kernels 
14 percent 



1 kernel 








1 kernel 







5 percent 



1 kernel 







12 kernels 

13 " 
46 " 


I 

6 


kernel 
kernels 


15 kernels 

20 

69 " 





7 


kernels 


64 kernels 

6 percent 

157 kernels 


4 
16 

10 


kernels 
it 

ii 


21 percent 
69 " 

70 


13 
17 
21 


percent 
it 

M 


18 percent 
28 " 
26 " 


13 

4 

74 


percent 
ii 
ii 



1 The range of the relative humidity of storage from 
percent) . 

2 Color of the rice in mass . 

3 Mean of 5 samples. 

4 Rough rice smelled musty before milling. 

5 Insufficient head rice for analysis. 



A (62-75 percent) through E (100 



15 



TABLE 7. — Summary of some factors measuring the cooking quality of the head rice from 
samples of rough rice stored at different relative humidities for various periods 



Treatment and 
storage period 1 



BEPT 



Amy- 
lose 



Reducing 
sugars 



Nonreducing 
sugars 3 



Cooking _ 

/ Remarks 



13. 4$ prestorage 
moisture content: 

Prestorage check 
days 

A: 

45 days 

87 " 

186 " 

B: 

45 days 

87 " 

186 " 

C: 

45 days 

87 " 

186 " 

D: 

45 days 

87 " 

186 " 

E: 

45 days 

87 " 

186 " 6 

23.6$ prestorage 
moisture content: 

Prestorage check 
days 

A: 

45 days 

87 " 

186 " 

B: 

45 days 

87 " 

186 " 

C: 

45 days 

87 " 

186 " 

D: 

45 days 

87 " 

186 " 

E: 

4-5 days 

87 " 

186 " 6 

LSD (.05) 
(.01) 



73 

72 
71 
72 



72 
72 



74- 

72 
71 



75 
73 
70 



72 
73 5 



73 



75 
72 
71 



74 
71 
72 

74 
73 
72 



74 

72 
72 



72 



0.9 
1.2 



Percent 



22.7 

21.5 
22.4 
26.5 



22.6 
22.1 
24.6 



23.8 
21.8 
23.7 



22.5 
22.9 

24.7 



22.6 
23.1 



22.1 



21.3 
22.9 
25.1 



22.7 
23.1 
25.0 

22.9 
24.3 
24.7 



22.9 
22.8 
24.0 



24.2 
23.4 



Percent 



5.C 

2.5 
5.0 
2.5 



5.0 
5.0 
5.0 



7.5 
5.0 
7.5 



10.0 
22.5 
33.5 



7.5 
20.0 



2.5 



5.0 
7.5 
2.5 



7.5 
5.0 
5.0 



15.0 
20.0 
22.5 



5.0 
10.0 



Percent 



7.5 

10.0 
15.0 
10.0 



17.0 

21.5 

5.0 



15.0 

21.5 

7.5 



26.5 
46.5 
34-. 



10.0 
31.5 



12.5 



12.5 

19.0 

7.5 



12.5 

24.0 

7.5 

12.5 

17.0 

7.5 



10.0 
12.5 
10.0 



10.0 
21.5 



Percent Percent 



White 
White 



White 



White 



White 



White 



White 
White 



White 



White 



White 7 

Cream 

Yellow 



Cream 7 
Yellow 



The range of the relative humidity of storage from A (62-75 percent) through E 
(100 percent) . 

Mgms. maltose per 10 g. flour. 

Mgms. sucrose per 10 g. flour. 

1 (good) to 7 (poor) . 

Broken kernels used for determination. 

Insufficient head rice for analysis. 

Many discolored grains. 



- 16 -