Also available as PDF (figures and tables appear in the PDF).
Background: Dietary therapy through a low-protein diet (LPD) has long been used for preserv-ing the renal function of patients with chronic kidney disease (CKD). Reducing the amount of protein ingested from rice would make it possible to allocate the difference to side dishes, thereby improving the quality of meals and facilitating adherence to LPD. Methods: Forica Foods Co., Ltd., Uonuma City, Niigata, Japan developed exclusive technology in 1994 for obtaining low-protein rice (LPR), using proteolytic enzymes to digest and remove the protein in white rice. In 2004, we developed processing technology to enhance the palat-ability of said LPR. By combining these technologies, we established a manufacturing method for producing delicious, high quality processed rice products which can serve as a daily staple. Results: For more than two decades since being launched in 1995, nearly 100 million Protein Low Content (PLC) rice products have been sold, and to date, there have been zero complaints of health problems attributable to them. This demonstrates their high safety even when eaten repeatedly over a long period. Discussion: The PLC Rice series of products, which compare favorably with, and can be sub-stituted for, regular rice, are delicious (high quality) enough to be eaten everyday. They enhance the quality of mealtimes for CKD patients by increasing their range of food choices. Conclusion: PLC Rice product offers high added value, as they not only facilitate adhesion to LPD but also add satisfaction and contentment to daily meals, helping to enhance the quality of life (QoL) of patients with CKD.
Keywords: Chronic kidney disease (CKD); Low-protein diet (LPD); Low-protein rice (LPR); Dietary therapy
Dietary therapy through a low-protein diet (LPD) has long been used to preserve the renal func-
1-3 tion of patients with chronic kidney disease (CKD).1-3 LPD restricts the amount of protein in
the total dietary intake and it lowers the production of urea nitrogen, an end product of protein
metabolism.4 It is considered that the level of protein intake modulates the filtration load on
5,6 the kidneys and tempers the decline of renal function.5,6 Over the past 50 years, LPD have been
successfully used to treat chronic renal failure in Japan. Since the easiest course of action is to
cut down on foods which are high in protein, the main dishes, such as meat and fish, are usually
reduced to smaller servings. However, such frugality compromises the quality of meal times.
Removing protein from rice would minimize the need to cut down on main dishes.
Mealtime quality would be maintained, making it easier for pa-
tients to follow the LPD.
To address this issue, in 1992 the Niigata Agricultural
Research Institute Food Research Center developed a technol-
ogy (JP2706888B) using lactobacillus fermentation to reduce
the protein, phosphate, and potassium contained in white rice
(WR).8 However, their method posed technical challenges such
as extremely long processing times and the difficulty of mi-
croorganism control hampering reliable production. In 1994,
Forica Foods Co., Ltd., Uonuma City, Niigata, Japan built on
this technology to develop an exclusive proteolysis technology
(JP3156902B) utilizing an enzyme product which can break
down protein in WR more quickly and reliably than lactobacilli
fermentation.9 The following year, the manufacture and sales of
“Cooked PLC Rice 1/3 (PLC: Protein Low Content)” began.
PLC Rice is processed, protein reduced WR. The palat-
ability (quality) of this low-protein rice (LPR) is such that it can
be eaten day after day. The PLC Rice products were developed
to facilitate adhesion to the LPD, thereby improving the quality
of life (QoL) of patients with CKD. In this article, the manufac-
turing process for the PLC Rice series will be described.
Raw materials are WR, pH adjuster, and protease.
There is no particular restriction on the type of WR. For
example, either Japonica rice (short grain) or Indica rice (long
grain) can be used. Highly clean raw material is used to reduce
the risk of microbiological contamination.
In the protein digesting step, the temperature and pH
must be maintained for a certain amount of time at levels con-
ducive to enzyme activity. To prevent in-process microbiologi-
cal proliferation and consequent product contamination, it is
desirable to keep the reaction solution pH acidic and at or above
50 °C. To control pH, a suitable quantity of organic acid is add-
ed. Suitable organic acids include citric acid, lactic acid, fumaric
acid, gluconic acid, and glucono delta-lactone (GDL). Out of
these, citric acid is chosen because of its high buffering property,
ability to maintain pH within the enzyme solution stably over a
long period, and for having the smallest negative effect on the
taste and aroma of cooked rice.
As proteolytic enzyme, acidic protease approved by the
Ministry of Health, Labour and Welfare (MHLW) as a food ad-
ditive and available on the market is used. In our method, we
use an enzyme mix (EM) consisting of an exclusive formula-
tion of at least 3 kinds of enzyme products, comprising at least
1 each derived from Aspergillus oryzae, Rhizopus niveus, and
Aspergillus niger respectively. Each enzyme product is a crude
enzyme product extracted from the source microorganisms, and
the main component is protease in the aspartic protease family
(EC 3.4.23).
The protein digesting process is broadly divided into enzyme
digestion and washing. In the first step, surface bran residue
and germs were washed away with water. The washed WR is
placed in a reaction solution containing dissolved EM and citric
acid, and allowed to soak for a certain period of time (up to 24
hours) in a temperature and pH conducive to enzyme activity.
This breaks down the protein in the WR. Subsequently, thorough
washing removes any unnecessary matter: rice protein decom-
position product, EM, and excess citric acid. These steps yield
LPR (Raw LPR), which is raw, protein reduced WR.
Figure 1 shows the time lapsed changes of protein mass
in rice treated with enzyme with a single protease derived from
Figure 1. The Effect of Processing Time and Enzyme Concentration on Protein Removal. ) 7
c 2
P 0
0 6 12 18 24 30 36
0.01% (w/v) 0.05% (w/v) 0.1% (w/v)
Aspergillus oryzae. Protein mass in rice is highly dependent on
enzyme concentration and reaction time. By adjusting these fac-
tors, the rice protein mass can easily be reduced to target levels.
In the actual process of protein enzyme treatment, EM is used
instead of a single enzyme, resulting in better removal rates and
production efficiency compared to a single enzyme. This is like-
ly to be because the combination of multiple enzymes each with
different protein cleavage sites reduces the molecular weight of
the decomposition product. The smaller the molecular weight of
rice protein, the easier it is to elute from the rice grain.
The manufacturing flow of these products is outlined in Figure
2. Regardless of product form, low protein rice products need to
have their rice protein content broken down and removed. The
method employed by Forica Foods is based on the invention by
Nakajo et al (JP3156902B), and consists of utilizing protease to
process protein.9 The very simple production process is shared
across product forms.
The Raw LPR obtained by said protein digestion process re-
quires special techniques and know-how to produce rice grains
which maintain their shape while offering palatability. This is
because Raw LPR grains are extremely fragile, and when sub-
jected to steaming or cooking like ordinary WR, they dissolve
into a gruel-like mass which is far from delicious. In order to
solve this problem, we developed a method (WO 2017037799
A1) for processing LPR into a palatable, high quality product.10
The manufacturing method for “Cooked PLC Rice” can be
Figure 2. Production Flow Chart of PLC Rice.
broadly categorized into cooking, hot water injection, sealing,
and cooling. In the first step, each serving of the Raw LPR is
filled into heat resistant containers. Without adding water, the
containers are transported to our exclusive rice steamers in-
stalled in clean rooms. The rice steamer chamber is sealed and
the interior de-aired to create a vacuum. Immediately, steam is
injected powerfully to instantly raise the temperature within the
chamber to 130 °C to 140 °C. This state maintained for 30 to 120
seconds during which the rice is steamed rapidly. Immediately
after steaming the rice, sterile hot water of at least 90 °C is added.
The steamed LPR is promptly sealed by heat resistant film with
oxygen absorber affixed to it. The temperature is maintained for
an additional 5 to 10 minutes to ensure thorough steaming of the
content. Subsequently, the packaged rice is allowed to air cool
gradually for 20 to 30 minutes until its temperature reaches 30
to 35 °C, then subjected to X-ray inspection to check for foreign
matter and weighed. Articles which pass the inspections become
product.
Using the steaming method described above, in which
rice is steamed by elevating the temperature in the chamber in-
stantaneously without adding water, the starch can be prevented
from eluting from the Raw LPR, thereby avoiding loss of the
flavor of white rice and making it possible to obtain low protein
rice with appropriate viscosity and elasticity that is suited to Jap-
anese preferences. In addition, the hot water injection process
makes it possible to change the amount of added water at will.
Thus, the moisture content of the product can be adjusted easily
to obtain the desired hardness/softness of the cooked rice. As has
been described, this technique is an extremely unique method of
cooking rice which offers both practicality and flexibility.
The manufacturing method for “Semi-Cooked PLC Rice” can be
broadly categorized into steaming, drying, and flaking to sepa-
rate into individual grains. The most basic manufacturing meth-
od consists of spreading out Raw LPR into a uniform thickness,
steaming with steam, then loosely separating the grains, drying
uniformly overall, then flaking to separate the rice grains into
individual grains. By gelatinizing and then drying the raw starch
contained in Raw LPR, it is possible to obtain “Semi-Cooked
LPR” whose rice grains are strong enough for long-term storage
and which can be cooked similarly to WR.
However, simply steaming the rice with saturated steam
results in highly viscous starch eluting from the surface of the
LPR grains. This causes the LPR grains to stick strongly to each
other, making it extremely difficult to separate the grains into
uniform size. Variations in the size of LPR clusters can cause
uneven drying. Trying to separate unevenly dried LPR clusters
generates large quantities of cracked and crushed rice, resulting
in significant loss of productivity. Furthermore, when LPR thus
obtained is cooked, it is stickier than necessary, compromising
the quality of the product.
To solve the issues of productivity and reliable product
quality, we invented the 2 processing methods shown below.
Refrigeration to retrograde the starch: Raw LPR is spread out
evenly into a thickness of 30 to 50 mm, then steamed for 5 to 10
minutes with saturated steam. This is transferred to a refrigerator
and kept at 0 to 5 °C for 24 to 72 hours. This causes the starch,
gelatinized by steaming, to retrograde, resulting in weakened ad-
hesion between rice grains, thereby facilitating the flaking pro-
cess. After the grains are separated, the rice is uniformly dried
to bring the moisture content of the grains to 15 to 26%. The
separated LPR grains are screened for grain shape and color, and
the grains with uniform shape and color are weighed and sealed
in packaging material together with oxygen absorber to obtain
product.
Superheated steam: Raw LPR is spread out evenly into a thick-
Table 1. Nutrient Content in 100 Grams of “Cooked PLC Rice” Products.
Calories kcal 168 160 (3.1)
Moisture % 60.0 60.4 (0.7) 60.1 (1.7) 60.1 (0.8) 60.5 (1.6) 60.6 (0.5)
Total Protein % 2.5 0.87 (0.1) 0.44 (0.0) 0.24 (0.1) 0.13 (0.0) 0.10 (0.0)
Total Fat % 0.3 0.5 (0.1)
Total Carbohydrate % 37.1 38.1 (0.7) 38.9 (1.7) 39.0 (0.7) 39.1 (1.4) 38.8 (0.7)
Ash % 0.1 0.1 (0.0)
Sodium mg 1 2 (0.3)
Potassium mg 29 0.6 (0.3)
Calcium mg 3 5 (0.0)
Phosphorus mg 34 15 (1.0)
ness of 30 to 50 mm, then steamed for 4 to 10 minutes using
superheated steam of at least 105 °C. The superheated steam,
obtained by heating saturated steam, makes it possible to heat
efficiently using higher temperatures than saturated steam.
Furthermore, superheated steam is drier than saturated steam,
thereby keeping down excess moisture in the rice during steam-
ing. Therefore, the steamed rice is less viscous and more easily
separated.
The subsequent steps are similar to method described
above. Immediately after steaming, the Steamed LPR is sepa-
rated loosely and dried by warm air so that the moisture level is
uniform throughout, at 16% to 20%. The rice is then separated
into individual grains using a cracking device, etc. The separated
LPR grains are screened for grain shape and color, and the grains
with uniform shape and color are weighed and sealed in packag-
ing material together with oxygen absorber to obtain product.
Compared to method using retrogradation, in which the
process is interrupted for the refrigeration step, this method con-
sists of fewer steps and is amenable to continuous production
conveyor-style. Therefore, it is possible to manufacture “Semi-
Cooked PLC Rice” efficiently.
Nutrition information on PLC Rice products is shown in Table
1. Test samples were taken from at least 3 separate production
days. As shown in the Table 2, there is minimal interlot vari-
ability of nutritional values, indicating extremely high repro-
ducibility. Particularly noteworthy is the protein content, which
demonstrates reliability in meeting the respective target values.
PLC Rice is LPR which is processed, protein reduced WR (Fig-
162 (6.8) 162 (2.6) 160 (7.1) 160 (1.7)
0.5 (0.1) 0.6 (0.1) 0.3 (0.1) 0.5 (0.2)
0.1 (0.1) 0.1 (0.1) 0 (0) 0 (0.1)
2 (0.0) 2 (0.2) 2 (0.1) 2 (0.1)
0.5 (0.2) 0.9 (0.2) 0.6 (0.1) 0.7 (0.2)
5 (0.3) 5 (1.2) 5 (0.7) 5 (0.6)
15 (1.5) 14 (1.0) 13 (0.7) 13 (1.2)
ure 3). Some of the products in the series have been approved
as “Food for special uses” by the Ministry of Health, Labour
and Welfare, and for bearing claims on the label that they are
suitable foods for kidney disease patients. In 1995, when we
launched the first product, it contained 1/3 of the protein in WR,
that is, 2/3 of the WR protein had been removed. With continued
technological development, we achieved a reduction rate of 1/25
by 2007. As of 2017, 22 years from its development in 1994,
the PLC Rice series consists of 10 products to accommodate
consumer needs in terms of product form, reduction rate (1/3 to
1/25), and serving size (140 to 180 grams).
PLC Rice comes in 2 product forms: “Cooked PLC
Rice” which can be microwaved or boiled in the pouch, and
“Semi-Cooked PLC Rice” which requires cooking in a rice
cooker. In “Cooked PLC Rice,” LPR is aseptically packaged. In
“Semi-Cooked PLC Rice,” LPR is steamed, dried, flaked, and
sieved, and requires a finishing step of cooking such as boil-
ing, steaming, or microwaving before serving. Both types of
products can be stored and distributed at room temperature. The
best-before date of “Cooked PLC Rice” is 7 months and “Semi-
Table 2. The Effect of Processing Time and Enzyme Concentration on Protein Removal.
0 7.4 7.4 7.4
5 6.9 5.9 5.5
24 6.3 4.1 2.9 Cooked PLC Rice” is 12 months.
Figure 4 shows the SDS-PAGE profile (CBB stain) of Raw LPR
extract. Compared to extract from non-treated WR (L1), Raw
LPR extract (L2) no longer shows any protein-derived bands ex-
cept for some in the low molecular weight side. There were no
bands common to Raw LPR (L2) and EM (L3), indicating that
enzyme derived protein is absent (or under the CPB stain detec-
tion limit). These results show that rice protein decomposition
product and EM are washed away from Raw LPR, leaving no
residue in the product.
To store the packaged “Cooked PCR Rice” safely in room tem-
perature, the contents must be sufficiently sterilized and sealed
in the sterile state. Raw LPR is steamed with high temperature,
high pressure steam in a steaming device installed in a clean
room. At the same time, it undergoes thorough sterilization under conditions which are equivalent to the 120 °C for 4 minutes
(F0=3.1) stipulated in the Japanese Food Sanitation Act for re-
tort pouch food. Subsequently, the contents are kept sterile while
sealing together with oxygen absorber, thereby securing sterility
of the product. In fact, since its adoption in 2004, there have
been no incidents of product spoilage or deterioration attribut-
able to insufficient sterilization, proving the efficacy and safety
of this technique.
According to our findings relating to “Pre-Cooked
PLC Rice,” drying steamed LPR to a moisture content of 15 to
26% yields desirable quality (particularly mouthfeel) when it
is cooked. By sealing this together with oxygen absorber and
maintaining an anaerobic state inside the package, it becomes
Figure 5. The Production Amount of PLC Rice.
Figure 4. CBB-Stained SDS-PAGE Patterns of the Raw LPR Extract. M; Marker (AE-1440, ATTO, USA), L1; 5-times concen- trated extract from non-treated rice, L2; 5-times concen- trated extract from Raw LPR, L3; EM, L4; Thermo-treated EM (50 °C, 24 hrs).
possible to store it safely at room temperature. However, once
the package is opened, new oxygen flows into the package. The
anaerobic state cannot be maintained and there is risk of mold
and other microbiological growth. A product with moisture level
higher than 20% requires refrigeration or freezing. However, a
product dried to a moisture level of 16% to 20% can be stored
safely at room temperature. This is due to the reduced water ac-
tivity of the product, which prevents mold etc. from proliferating
after the package is opened.
Quantities of PLC Rice produced from launch to the present day
are shown in Figure 5. In more than 20 years since its launch,
ud 5
re 4
E 2
1996 1997 1998 1999200020012002200320042005 2006 2007 2008 2009201020112012201320142015 2016
nearly 100 million PLC Rice products have been provided to
CKD patients through many hospitals throughout Japan. Al-
though sales have declined since the peak of 7.5 million servings
in 2000, the quantities have been growing gradually since 2004
when the above-mentioned high temperature steaming method
was adopted. As of 2016, we are producing the equivalent of 4.7
million servings annually.
In the 22 years of producing and selling “Cooked PLC
Rice” and the 7 years of “Semi-Cooked PLC Rice,” there have
been zero reports of health problems attributable to these prod-
ucts. Given the high frequency of LPD Rice ingestion by CKD
patients who eat it every day as part of their LPD, and the fact
that PLC Rice products are composed almost entirely of natural
ingredients derived from WR, it is reasonable to say that PLC
Rice, regardless of product form, is safe to eat and has no nega-
tive health effects, even for CKD patients who ingest them re-
peatedly over the long-term.
From clinical findings, the recommended protein intake for Jap-
anese CKD patients is under 0.5 g/kg body weight (BW)/day.11
The cooked rice that is the staple for Japanese people contains
2.5% protein. If a person eats a bowl (approximately 165 g) of
cooked rice 3 times a day, he or she will ingest 12.5 g of protein
from the rice. A patient weighing 60 kg should ideally ingest
less than 30 g of protein per day. If the patient eats regular rice,
Figure 6. Relationship between Total Protein Allowance and Protein Intake from Staple Out of Total Protein Allowance.
Bars with solid outline: Protein intake when ingesting 165 g (1 serving) of regular rice or LPR 3 times a
day
Bars with dotted outline: Daily protein allowance (30 g/day)
White circle and solid line: Difference and percentage - Total protein allowance and protein intake from
staple out of total protein allowance
WR; White Rice, “1/3”; PLC Rice 1/3 (0.83 % protein), “1/5”; PLC Rice 1/5 (0.5 % protein), “1/10”; PLC
Rice 1/10 (0.25% protein), “1/20”; PLC Rice 1/20 (0.125% protein), “1/25”; PLC Rice 1/25 (0.1% protein)
it would account for 40% of the protein allowance. To keep with
the allowance, the entire meal plan needs to be adjusted.
Figure 6 shows the how different proportions of a hy-
pothetical patient’s daily protein allowance of 30 g is taken up
by eating the same 165 g (1 serving) of WR or PLC as the staple
food 3 times a day. Unprocessed WR translates to roughly 40%
of the daily protein allowance, thereby leaving only about 60%
to be allocated to side dishes (Figure 2). By contrast, LPR, even
at the reduction rate of 1/3, only accounts for 8.4% of the dai-
ly allowance, leaving more than 90% to be occupied by other
dishes. The smaller the reduction rate, the less protein from the
staple, thereby permitting the rest of the allowance to be filled by
other foods. This greatly expands the patient’s food choices.
Another dietary consideration for CKD patients is the
desirability of reducing phosphorus and potassium intake in ad-
dition to protein. At the same time, there is a need to ensure the
patient takes in enough nutrients, particularly energy. With PLC
Rice products, not only can protein intake be reduced to the de-
sired level, but the products contain 50% less phosphorus and
95% less potassium compared to regular cooked rice while of-
fering the same energy as WR. They meet all of the requirements
as a staple food for CKD patients (Figure 7).
We developed exclusive technology for digesting and
removing protein from WR using microorganism-derived en-
zyme product, and technology for processing the Raw LPR thus
30 100
0 0
WR "1/3" "1/5" "1/10""1/20""1/25"
/l ack 100 ( yg re n E
)t 40 c
udor p 29 g 30
001/ g m( t nn 20 et
noc m ui 10 ss at o P 0.6 0.5 0.9 0.6 0.7
obtained into a palatable food product. By combining these tech-
nologies, we can reliably manufacture delicious, high quality,
low protein rice product, which can be eaten repeatedly as sta-
ple. In the 20 years from its launch, nearly 100 million PLC Rice
products have been sold, with zero complaints relating to health
problems arising from their consumption to date. This demon-
strates their safety even when eaten repeatedly over a long pe-
riod.
The PLC Rice series of products, which compare favor-
ably with, and can be substituted for, regular rice, are delicious
(high quality) enough to be eaten everyday.
LPR enhances the quality of mealtimes for CKD patients by in-
creasing their range of food choices. It is therefore, reasonable
to say that PLC Rice products offer high added value, as it not
only facilitates adhesion to LPD but also add satisfaction and
contentment to daily meals, helping to enhance the QoL of pa-
tients with CKD.
All authors are employee of Forica Foods Co., Ltd., Uonuma
City, Niigata, Japan. All of this study and work has been per-
formed at the Forica Food Co., Ltd., Uonuma City, Niigata, Ja-
pan.
The authors appreciate to Dr. Shaw Watanabe (Life Science
)t 168 160 162 162 160 160 c 2.5
udor p g
001/ g( t ne t noc 0.87
ni et or 0.44 P 0.24 0.13 0.10
WR 1/3 1/5 1/10 1/20 1/25 WR 1/3 1/5 1/10 1/20 1/25
)t 40 c udo 34 r p g 30
001/ g m( tn et 20 15 15 noc 14 13 13 s ur
ohps
oh P
WR 1/3 1/5 1/10 1/20 1/25 WR 1/3 1/5 1/10 1/20 1/25
Promoting Association, Tokyo, Japan) for his great advices on
this study. The authors would also like to tahnk all the staff of
Institute of Food Research and Product Development Kasetsart
University (bangkok, Thailand), especially ms. Ngamjit Lowit-
hun and Mrs. patcharee Tungtrakul, for their helpful advice and
support to our research.. A part of this study was supported by
Grant from Japan International Cooperation Agency (JICA).