This winter "seasonal fruit" is available online, but many people have a "fear of buying"? Teach you how to choose →

Winter is coming, and it is the best time to eat grapefruits. However, many people suffer from "grapefruit phobia" - out of 10 grapefruits bought, 8 of them are bitter. I thought of learning the method circulated on the Internet to carefully distinguish the so-called "male" and "female" grapefruits, but the situation was not much better.

Image source: Wikipedia Commons

01 Why is grapefruit bitter?

To answer this question, let’s first think about where the bitter taste of grapefruit comes from. Studies have shown that grapefruit contains flavor substances such as naringin, limonin, vitamin C, organic acids, and sugars. The content and ratio of these substances determine the taste of grapefruit. [1]

The bitterness of grapefruit mainly comes from naringin and limonin, and the content of these ingredients depends on the variety. [1] According to incomplete statistics, there are more than 200 varieties of grapefruit on the market, [2] and varieties with too high naringin content will naturally have a stronger bitter taste.

Naringin molecular model (Image source: Wikipedia commons)

The sweetness of grapefruit mainly comes from sugar. As we all know, the sweetness of Xinjiang fruit is closely related to the geographical conditions in which it is grown. The amount of sugar and the type of sugar that grapefruit can accumulate are also closely related to the growing conditions, especially temperature and light. [3]

When the grapefruit is ripe and picked by farmers, the cells in the grapefruit are still active to a certain extent. They will metabolize substances and change the composition of the grapefruit to a certain extent. Therefore, the storage time and conditions will also affect the taste of the grapefruit. [4]

02 How to choose the pomelo of your dreams?

First, choose the right variety.

Different varieties of grapefruit are available at different times of the year. Some are available as early as June, while others mature in November. Based on their sweetness, they can be divided into three categories: sweet, sweet and sour, and sour. [5,6] Therefore, before buying grapefruit, you should choose the right variety based on time and taste.

Examples of excellent grapefruit varieties (Image source: self-made by the author; data source: "Illustrated Guide to High-yield and High-quality Cultivation and Pest and Disease Control of Citrus")

When you go shopping in supermarkets or online stores, you can ask the salesperson about the variety of grapefruit, and you can also use some ready-made logos. For example, many grapefruits are national geographical indication products, and there will be corresponding logos on the packaging.

Second, judge the growing conditions of grapefruit by its appearance.

Next, you can refer to the Citrus Grade Specifications to determine the quality of the grapefruit. Grapefruit grown under ideal conditions will have smooth skin with fewer wounds, mold spots, and traces of drugs. [7]

Third, try to choose fresher grapefruits.

If you hold a grapefruit in your hand, it is heavier than grapefruits of similar size; if you gently press the peel, it feels firmer and has no swelling or water retention. Generally speaking, it is a fresh grapefruit.

In addition, some regions have also issued relevant special standards. For example, Shanghai has issued the "Shanghai Fruit Grades", which stipulates the sweetness of citrus fruits - special grade is the sweetest, first grade is the second sweetest, and second grade is the third sweetest. If you see such a sign, you can buy it with confidence. [8]

03 What should I do if I still feel bitter?

In fact, bitter substances in moderation are not bad things. For example, animal experiments have shown that naringin can promote insulin secretion. [9] Although this result cannot be directly applied to us, grapefruit itself is a low-calorie, nutritious food, and excessive pursuit of sweetness may be unhealthy.

Nutrition of grapefruit (Image source: Public Health Science Data Center)

Furthermore, whether something is bitter or not varies from person to person. On our taste cells, there is a special structure called a taste receptor. There are dozens of receptors responsible for detecting bitterness, all encoded by genes. [10] Therefore, a person's genetic makeup determines how they perceive bitterness. For example, studies have shown that people with certain genes are more sensitive to the bitterness of grapefruit juice. [11]

Common bitter foods and their related components (Image source: An overview of bitter compounds in foodstuffs: Classifications, evaluation methods for sensory contribution, separation and identification techniques, and mechanism of bitter taste transduction)

So, if you really don't like bitter taste, and you are "unlucky" enough to choose bitter grapefruit, can you still "save" it? There is a way:

First, naringin is not evenly distributed. Generally speaking, it is more in the peel and some in the syringa, but less in the flesh. [12] When peeling a grapefruit, try not to let the juice from the peel and syringa contaminate the flesh, and the bitterness will be less.

Secondly, you can add a little salt. This may sound strange at first. Wouldn’t adding salt to bitterness make it even more bitter? In fact, the sensitivity of taste receptors is not only related to genes, but also affected by the environment. Recent studies have shown that salt can interfere with bitter taste receptors, thereby reducing the bitterness of certain substances. [13]

Of course, a word of caution is in order: the Chinese Dietary Guidelines recommend that adults should not consume more than 5g of salt per day. [14]

04 Are there any other precautions when eating grapefruit?

Citrus fruits may interfere with certain oral medications.

There are two steps for oral drugs to work: first, the whole drug is exposed to the active ingredients under the action of certain enzymes; second, the active ingredients reach the inside of cells through some pathway. However, citrus fruits, such as grapefruit, may interfere with the above two steps: either promoting the decomposition of drugs, resulting in excessive drug concentrations and adverse reactions; or hindering drug transport, so that the concentration required for treatment cannot be reached.

The severity of adverse reactions depends on the medication, physical condition, and amount of grapefruit juice consumed. Some people may experience mild adverse reactions, but for people over 70 years old, they may be very serious. [15–18]

Drug interactions (Image source: author’s own)

Therefore, we would like to remind everyone that although grapefruit is good, not everyone can eat it. Especially for the elderly, when taking prescription drugs, they should strictly follow the doctor’s instructions, and when taking over-the-counter drugs, they should also read the instructions carefully. [19]

Author: Zhao Yanchang, member of China Science Writers Association

Reviewer: Wang Guoyi, Postdoctoral Fellow in Nutrition and Food Safety at China Agricultural University, Associate Professor at Beijing University of Technology, Chairman of the Elderly Food and Health Committee of Beijing Food Society

Produced by: Science Popularization China

References

[1] Luo Yi, Li Wenyun, Wang Xiaoke, et al. Analysis and evaluation of fruit quality of 10 local pomelo resources in Guizhou [J/OL]. Seed, 2021(5): 78-83, 90. DOI:10.16590/j.cnki.1001-4705.2021.05.078.

[2] The creative team of "Chinese Plants that Influence the World". Chinese Plants that Influence the World [M/OL]. Sichuan Science and Technology Press, 2019 [2024-10-24]. https://book.douban.com/subject/34838588/.

[3] Chun Changpin. Illustration of high-yield and high-quality cultivation and pest and disease control of citrus[M/OL]. Chemical Industry Press, 2016[2024-10-23]. https://weread.qq.com/web/reader/3153254071c964663153b18kc9f326d018c9f0f895fb5e4.

[4] Yuan Qi, Yao Xiaoling, Feng Guiren, et al. Effects of temperature and gas conditions on the bitterness of pomelo during refrigeration[J]. Food Science, 2013(22): 303-306.

[5] Zhang Taiping, Peng Shaolin, Wang Zhengfeng, et al. Preliminary study on classification and identification of pomelo germplasm resources[J]. Ecological Science, 2001(3): 1-7.

[6] Li Xiaoting. Evaluation and analysis of 45 grapefruit germplasm resources[D/OL]. Fujian Agriculture and Forestry University, 2018[2024-10-24]. https://kns.cnki.net/KCMS/detail/detail.aspx?dbcode=CMFD&dbname=CMFD201801&filename=1017067534.nh.

[7] Ministry of Agriculture of the People’s Republic of China. Citrus grade specifications: NY/T 1190—2006[S/OL]. (2006-12-06)[2024-10-24]. https://std.samr.gov.cn/hb/search/stdHBDetailed?id=B3A3E8BA79A375ACE05397BE0A0A6F11.

[8] Shanghai Municipal Administration for Market Regulation. Shanghai Fruit Grade Citrus: DB31/T 1131—2019[S/OL]. (2019-01-09)[2024-10-24]. https://std.samr.gov.cn/db/search/stdDBDetailed?id=F5D19067C3E948C2E05397BE0A0A6F91.

[9]FALOBI AA, FALANA AB, OFOSU WA, et al. Mechanisms Underlying the In Vitro Insulin Secretory Actions and In Vivo Antidiabetic Effects of Grapefruit's Naringin[J/OL]. Metabolism - Clinical and Experimental, 2020, 104[2024-10-25]. https://www.metabolismjournal.com/article/S0026-0495(19)30311-7/abstract. DOI:10.1016/j.metabol.2019.12.044.

[10]AHMAD R, DALZIEL J E. G Protein-Coupled Receptors in Taste Physiology and Pharmacology[J/OL]. Frontiers in Pharmacology, 2020, 11: 587664. DOI:10.3389/fphar.2020.587664.

[11]HAYES JE, WALLACE MR, KNOPIK VS, et al. Allelic Variation in TAS2R Bitter Receptor Genes Associates with Variation in Sensations from and Ingestive Behaviors toward Common Bitter Beverages in Adults[J/OL]. Chemical Senses, 2010, 36(3): 311. DOI:10.1093/chemse/bjq132.

[12] Zhang Shengyuan, Chen Weiling, Wang Nan, et al. Determination of mineral elements, total phenols, and naringin content and antioxidant activity in different parts of six kinds of pomelo [J/OL]. Food and Fermentation Industries, 2023(18): 105-112. DOI:10.13995/j.cnki.11-1802/ts.032761.

[13]KUMAR P, BEHRENS M. Influence of Sodium Chloride on Human Bitter Taste Receptor Responses[J/OL]. Journal of Agricultural and Food Chemistry, 2024, 72(18): 10531-10536. DOI:10.1021/acs.jafc.3c08775.

[14] Chinese Nutrition Society. Dietary Guidelines for Chinese Residents (2022) [M/OL]. People's Medical Publishing House, 2022 [2023-07-20]. https://book.douban.com/subject/35885945/.

[15]BAILEY DG, DRESSER G, ARNOLD JM O. Grapefruit–medication interactions: Forbidden fruit or avoidable consequences?[J/OL]. CMAJ: Canadian Medical Association Journal, 2013, 185(4): 309. DOI:10.1503/cmaj.120951.

[16]COMMISSIONER O of the. Grapefruit Juice and Some Drugs Don't Mix[J/OL]. FDA, 2021[2024-10-25]. https://www.fda.gov/consumers/consumer-updates/grapefruit-juice-and-some-drugs-dont-mix.

[17] Guidelines for rational medication in heart failure (2nd edition)[J]. Chinese Journal of Medical Frontiers (Electronic Edition), 2019, 11(7): 1-78.

[18] Chinese Medical Association Cardiovascular Disease Branch, Chinese Society of Biomedical Engineering Heart Rhythm Branch. Chinese Guidelines for the Diagnosis and Treatment of Atrial Fibrillation[J/OL]. Chinese Journal of Cardiovascular Diseases, 2023, 51(6): 572-618. DOI:10.3760/cma.j.cn112148-20230416-00221.

[19] Expert consensus on safe management of polypharmacy in the elderly [J/OL]. Chinese Journal of General Practice, 2018, 21: 3533-3544. DOI:10.12114/j.issn.1007-9572.2018.00.225.