“Newmai Cup” Jiangnan University Outstanding Case Analysis | Investigation of Moisture Distribution Changes in Frozen Rice during Different Cold Storage Periods

Ding Dong~
The second edition of the “NewMay Cup” Jiangnan University Outstanding Case Analysis is here!

We sincerely thank all our research partners and industry colleagues for your continued attention. Today, we are excited to present another remarkable study from the competition: “Investigation of Moisture Distribution Changes in Quick-Frozen Rice During Different Frozen Storage Periods”.

Development and Challenges of the Quick-Frozen Rice Industry

The quick-frozen rice industry, a significant branch of modern food manufacturing, has grown in response to consumers’ increasing demand for convenient, safe, nutritious meals that closely resemble freshly cooked rice. Freezing technology effectively suppresses microbial growth and biochemical reactions, ensuring food safety and extending shelf life. This aligns with the modern fast-paced lifestyle that requires convenient, healthy staple foods. The industry’s development trend focuses on producing higher-quality products that maintain water retention, texture (e.g., firmness, elasticity), and taste even after prolonged frozen storage.

However, the industry faces key challenges related to quality degradation during freezing, storage, and thawing. Moisture migration and recrystallisation are critical factors. During frozen storage, water in the rice forms ice crystals, causing uneven moisture distribution and increased free water content. This reduces water-holding capacity, hardens rice grains, and creates a coarse texture (e.g., altered stickiness and firmness), ultimately affecting consumer acceptance. Ensuring stable water states and texture during frozen storage is essential for enhancing product quality and driving industry advancement.

Investigation of Moisture Differences in Frozen Rice

This study employed advanced techniques to examine differences in water states of rice treated in two ways (endosperm retained vs. fully milled) during frozen storage and to understand how these differences relate to texture stability. Low-field Nuclear Magnetic Resonance (LF-NMR) and Magnetic Resonance Imaging (MRI) were used to non-destructively analyse water states (bound water, immobilised water, and free water content and distribution) and their dynamic changes throughout storage.

Figure 1: Principle of LF-NMR Analysis

Experimental Procedure

The study selected three representative rice types/treatments for comparison: fully milled Nanjing 9108 rice (NJ9108), Akita Komachi rice (QTXT), and endosperm-retained Nanjing 9108 rice (PYM).

1. Sample Preparation: Cook the rice, freeze it, and collect samples at designated storage times (0d, 14d, 30d, 60d).

2. Moisture Analysis: Use LF-NMR to measure water relaxation characteristics at each storage time point, calculate the proportion of different water states (particularly changes in free water T₂₂), and employ MRI to visualise the uniformity of water distribution.

Figure 2: T2 Relaxation Time Distribution of Quick-Frozen Rice

Figure 3: MRI of Water Distribution

3. Comparison Focus: Differences in water states (especially free water content and distribution uniformity) during prolonged frozen storage.

Figure 5: SEM Observations of Frozen Rice Structure

5. Fully milled white rice shows enlarged hydrated regions forming lateral cracks.

6. Endosperm-retained rice exhibits water distribution closer to freshly cooked rice.

Figure 4: Freeze-Thaw Curves and Freezable Water Content Changes

Figure 5: SEM Observations of Frozen Rice Structure

4. Uneven water distribution observed in rice during extended storage.

5. Fully milled white rice shows enlarged hydrated regions forming lateral cracks.

6. Endosperm-retained rice exhibits water distribution closer to freshly cooked rice.

Figure 4: Freeze-Thaw Curves and Freezable Water Content Changes

Figure 5: SEM Observations of Frozen Rice Structure

3. Hydration differences induced by ice recrystallisation persist even after reheating.

4. Uneven water distribution observed in rice during extended storage.

5. Fully milled white rice shows enlarged hydrated regions forming lateral cracks.

6. Endosperm-retained rice exhibits water distribution closer to freshly cooked rice.

Figure 4: Freeze-Thaw Curves and Freezable Water Content Changes

Figure 5: SEM Observations of Frozen Rice Structure

2. Endosperm-retained rice maintains relatively stable hydration, with slight increases in water mobility.

3. Hydration differences induced by ice recrystallisation persist even after reheating.

4. Uneven water distribution observed in rice during extended storage.

5. Fully milled white rice shows enlarged hydrated regions forming lateral cracks.

6. Endosperm-retained rice exhibits water distribution closer to freshly cooked rice.

Figure 4: Freeze-Thaw Curves and Freezable Water Content Changes

Figure 5: SEM Observations of Frozen Rice Structure

1. Decreased hydration and increased water mobility in fully milled rice.

2. Endosperm-retained rice maintains relatively stable hydration, with slight increases in water mobility.

3. Hydration differences induced by ice recrystallisation persist even after reheating.

4. Uneven water distribution observed in rice during extended storage.

5. Fully milled white rice shows enlarged hydrated regions forming lateral cracks.

6. Endosperm-retained rice exhibits water distribution closer to freshly cooked rice.

Figure 4: Freeze-Thaw Curves and Freezable Water Content Changes

Figure 5: SEM Observations of Frozen Rice Structure

Experimental Findings:

1. Decreased hydration and increased water mobility in fully milled rice.

2. Endosperm-retained rice maintains relatively stable hydration, with slight increases in water mobility.

3. Hydration differences induced by ice recrystallisation persist even after reheating.

4. Uneven water distribution observed in rice during extended storage.

5. Fully milled white rice shows enlarged hydrated regions forming lateral cracks.

6. Endosperm-retained rice exhibits water distribution closer to freshly cooked rice.

Figure 4: Freeze-Thaw Curves and Freezable Water Content Changes

Figure 5: SEM Observations of Frozen Rice Structure

Experimental Findings:

1. Decreased hydration and increased water mobility in fully milled rice.

2. Endosperm-retained rice maintains relatively stable hydration, with slight increases in water mobility.

3. Hydration differences induced by ice recrystallisation persist even after reheating.

4. Uneven water distribution observed in rice during extended storage.

5. Fully milled white rice shows enlarged hydrated regions forming lateral cracks.

6. Endosperm-retained rice exhibits water distribution closer to freshly cooked rice.

Figure 4: Freeze-Thaw Curves and Freezable Water Content Changes

Figure 5: SEM Observations of Frozen Rice Structure