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Feature Article

Phytohaemagglutinin Poisoning

Beans are one of the most versatile and commonly eaten nutritious foods throughout the world.  However, the consumption of common beans (e.g. green beans and French beans) and other beans (e.g. red kidney beans and white kidney beans) without proper processing may cause food poisoning due to the naturally present toxin phytohaemagglutinin.  This article gives a brief introduction on phytohaemagglutinin poisoning.

Phytohaemagglutinin toxin in beans?

Lectins are widely occurring, sugar-binding proteins that perform a variety of biological functions in plants and animals.  However, some of them may become toxic at high levels.  Among the lectins known to have toxic effects is phytohaemagglutinin, which occurs at relatively high levels in the seeds of legumes (i.e. beans).  Phytohaemagglutinin serves as defence against plant pests and pathogens. 

Phytohaemagglutinin, as its name implies, can agglutinate many mammalian red blood cells and interfere with cellular metabolism.  Moreover, it is an antinutrient, which can interfere with the absorption of minerals, particularly calcium, iron, phosphorus and zinc. 

Phytohaemagglutinin is found in many beans, but its level varies among different species of beans.  The concentration of phytohaemagglutinin is the highest in red kidney beans (Phaseolus vulgaris).  White kidney beans, another variety of P. vulgaris, contain about one-third the amount of toxin as does the red variety.  On the other hand, broad beans (Vicia faba) contain only 5% to 10% of the amount of phytohaemagglutinin that red kidney beans contain.  Some commonly consumed beans in Hong Kong, including soya beans , green beans and yard-long beans, have been reported to cause phytohaemagglutinin poisoning in other places.  To avoid food poisoning, all beans should be cooked properly before consumption since different cultivars of the same species might have significantly varying levels of the phytohaemagglutinin toxin..

Some commonly consumed beans in Hong Kong that have been reported to cause phytohaemagglutinin poisoning in other places

Clinical presentation of phytohaemagglutinin poisoning

Symptoms of phytohaemagglutinin poisoning include severe stomachache, vomiting and diarrhoea.  Some of the characteristics of phytohaemagglutinin poisoning are summarised in the table below:

Characteristics of Phytohaemagglutinin Poisoning


Generally not fatal.

Toxic dose:

As few as four to five raw beans can trigger symptoms.

Onset time:

Usually begins with gastrointestinal illnesses within one to three hours after ingestion of the food, with subsequent diarrhoea within that timeframe.


Upper and lower gastrointestinal illnesses. Vomiting may become severe. In addition to vomiting and diarrhoea, some people may have abdominal pain.


Spontaneous recovery usually occurs within three to four hours after the onset of symptoms, although some cases require hospitalisation.


All people, regardless of age or gender, are equally susceptible. The severity depends on the dose ingested.

How to prevent phytohaemagglutinin food poisoning from consuming raw beans

Methods of toxin reduction

Cooking with moist heat can reduce the toxicity of phytohaemagglutinin.  Compared with fully cooked kidney beans, raw kidney beans could have phytohaemagglutinin levels that are hundreds of times higher.  Therefore, the consumption of phytohaemagglutinin-containing beans is not a cause for concern as long as they are sufficiently cooked.  Extra care, however, should be exercised when phytohaemagglutinin-containing food is prepared at high altitudes where the boiling point is lower, when low heat cooking methods are employed or in situations where heat transfer is uneven. 

To destroy the phytohaemagglutinin toxin, beans should be soaked and boiled thoroughly in fresh water (e.g. soaked for at least 12 hours and then boiled vigorously for at least 10 minutes in water).  Previous studies showed that the phytohaemagglutinin toxin remained active even after the beans had been cooked at 85°C for an hour.  Therefore, beans should not be cooked at a low temperature, for example in a crock pot or slow cooker, since it may not destroy the toxin.  On the other hand, commercially tinned beans are safe to eat without further cooking as they have been subjected to thorough heat treatment.

Food safety limit on phytohaemagglutinin

Phytohaemagglutinin has not been evaluated by food safety regulatory authorities including the Joint FAO/WHO Expert Committee on Food Additives (JECFA), nor a health-based guidance value has been established for risk assessment.  Moreover, no relevant food safety standard has been established by the Codex Alimentarius Commission either.  Nevertheless, it has been reported that ingestion of as few as four to five raw beans can trigger symptoms.  Crucially, cooking with moist heat can remove the toxicity of phytohaemagglutinin.  Consumers should not eat raw or inadequately cooked beans. 

Key points to note

Advice to consumers

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Tips for Travellers: Lessons from a Campylobacter Outbreak

In October 2023, the media reported that nearly 900 people were affected in a massive food poisoning outbreak caused by Campylobacter species in Japan.  The incriminated food was nagashi sōmen, which are noodles flowing down a bamboo chute and being caught by diners with chopsticks as they float by.  The pathogen was detected in the spring water sending the noodles down the chute.  Travellers can savour local delicacies when travelling, but they should stay alert to threats to food safety.  Let’s learn more about Campylobacters in food and travel-related food safety tips in this article.


Campylobacters are commonly found in the intestinal tracts of animals and humans.  The most commonly reported Campylobacter species in human diseases is Campylobacter jejuni, followed by Campylobacter coli.  These disease-causing Campylobacter species can only grow at above 30℃ but can tolerate higher growth temperatures, and their optimum growth temperature is 42℃.  That said, Campylobacters have higher survival rates in food stored under refrigeration compared to food stored at room temperature.  Moreover, a micro-aerobic environment, i.e. reduced oxygen environment, is favourable to the growth of most Campylobacter species.  Oxygen comprises approximately 21% of the atmosphere, while these bacteria grow optimally at oxygen concentrations ranging from 3% to 5%.  According to the literature, consuming as few as 500 Campylobacter cells can cause illnesses.

Diseases caused by Campylobacters

Gastrointestinal illnesses caused by Campylobacters can affect individuals of different age groups.  Among them, children below the age of 5 and young adults aged between 15 and 29 are more prone to gastroenteritis.  Its incubation period usually ranges from two to five days.  The most common symptoms include watery diarrhoea or bloody diarrhoea, abdominal pain, fever, headache, nausea and/or vomiting, which usually last for 2 to 10 days.  While most patients can recover on their own, some may need antibiotic treatment.  The infection may be fatal to those with weakened immunity.  In rare cases, the infection can be followed by long-term illnesses such as reactive arthritis and Guillain-Barré syndrome (GBS).  GBS is a disease in which the body’s immune system attacks the nerves.  GBS patients can experience muscle weakness or even paralysis for weeks.

Campylobacters in food

Campylobacters are commonly found in most warm-blooded animals such as poultry, cattle, pigs, sheep and dogs.  C. jejuni has a very varied reservoir but is mainly associated with poultry.  C. coli is predominantly found in pigs.  Inadequately cooked meats (especially poultry) is one of the sources of Campylobacters.

Other sources include unpasteurised milk and products, contaminated raw fruits and vegetables, contaminated water or cross-contaminated ready-to-eat food.  Animal faeces can contaminate lakes and streams; the consumption of contaminated water has contributed to a number of global outbreaks.  Fruits and vegetables can be contaminated through contact with soil or water containing animal faeces.

Making smart food choices during travelling

The outbreak mentioned above was traceable to contaminated spring water as the source of Campylobacters.  Consumers should make careful food choices while travelling and take the following precautionary measures against food- or water-borne illnesses:

Dining Out

Salmonella in Snack Food

A ready-to-eat marinated pig oviduct sampleNote 1 collected by the Centre for Food Safety (CFS) from a food shop in Sham Shui Po was tested positive for the pathogen, SalmonellaNote 2.  Upon investigation, it was suspected to be caused by cross-contamination of cooked food with raw food, possibly through unclean gloves.  The CFS has instructed the shop to suspend the sale of the food product concerned, provided food safety and hygiene education to the staff, and requested them to conduct thorough cleaning and disinfection. 

To prevent cross-contamination, food handlers should maintain good personal and environmental hygiene at all times. Wash hands properly before and after work and whenever changing job duties (e.g. handling food after handling rubbish) or when their hands get dirty.  Clean and disinfect utensils and equipment after use.  Use covered rubbish bins and empty them regularly.  Keep food covered during display and storage.  Cook food thoroughly and keep it out of the temperature danger zone.  Consumers should consume snack food as soon as possible after purchase.

Note 1: Relevant press release:
Note2: To learn more about Salmonella, please browse the webpage below:

Healthy Eating Basics and Smart Food Choices

Healthy Eating Basics

How to Interpret the Test Report on Plant-based Milk

Recent years has seen the launch of many beverages made with plant-based milk.  An organisation collected 39 samples of prepackaged plant-based milk (including almond milk, coconut milk, rice milk, oat milk and soy milk) on the market for food safety and nutrient content tests.

Listen to Our Mascots:

-       For the levels of pesticide residues and metallic contaminants detected as stated in the organisation’s report, the risk assessment of the CFS revealed that all samples would not be detrimental to health upon normal consumption and met the local legal requirements.
-       As for the cases concerning nutrition labels Note 1 referred to the CFS by the organisation, the CFS found three products suspected of violating relevant labelling regulations, and has instituted prosecution.  The test results were satisfactory for ten products and unsatisfactory for two products, and six products were no longer available for sale on the market.  The test results of the remaining ones have yet to be confirmed.

-       From 2020 to mid-2024, the CFS collected a total of more than 450 plant-based milk samples for chemical (including nutrition content) and microbiological tests.  Except for one non-prepackaged soy milk sample containing an excessive amount of Bacillus cereus, all the remaining samples passed the tests.  The CFS has published the results and taken follow-up action. 

Food Safety Reminders:

-       Members of the public are advised to read the nutrition labels on the packaging before purchase, choose plant-based milk products with relatively low sugar and fat content, and consume them as soon as possible once opened.  People with food allergy should read the food allergen information on the labels of plant-based milk products at the time of purchase.

Note 1 To learn more about nutrition labels, please visit the following thematic website:

Smart Food Choices

Stewed Steamed Rice with Conpoy and Egg

When it comes to cooking stewed steamed rice, butter and cream will come to mind, which may put many people off.  To give the rice a rich and fresh flavour, why not try the Chinese cooking method?  Seasoned with broth, this dish is just as healthy and tasty with nutritious eggs and vegetables as ingredients. 

Today's recommended “stewed steamed rice with conpoy and egg” dish requires careful thought to prepare despite the simple ingredients.  Eggs are a rich source of protein, comparable to meat.  Cooking the yolk and the white separately can preserve the eggs’ nutrients as well as highlight the colourful presentation of the dish. 

To find out how to cook the dish, please refer to the Department of Health's“Recipes”:

News on CFS

1.  CFS's Trade Talk on Glycidyl Fatty Acid Esters & 3-monochloropropane-1,2-diol Ester in Food

The CFS held a trade talk on Glycidyl Fatty Acid Esters & 3-monochloropropane-1,2-diol Ester in Food on 31 January 2024 to give information on these substances that are naturally produced during food processing, their sources in food, local recommendations and legal standards in respect of their concentrations, and previous risk assessment studies conducted by the CFS, etc.

2.  CFS's Official WhatsApp Channel Launched on 1 March
The CFS's official WhatsApp Channel was formally launched on 1 March.  Members of the public and the trade are welcome to click the link below or scan the QR code in the picture to check out the “Centre for Food Safety” WhatsApp Channel and press “Follow Now” to receive and share the latest and reliable information on food safety at any time.

3.  CFS's Zoom Cloud Meeting on “Food Safety in relation to Ready-to-Eat Foods Sold by Vending Machines”
Food vending machines provide a convenient way for customers to buy food.  However, improper temperature control and inadequate cleaning of processing/dispensing systems in vending machines can pose potential microbiological risks in the ready-to-eat foods sold.  Sale of unfit foods could lead to food poisoning and possible prosecution against the operator.  In view of this, the specially CFS held a Zoom Cloud Meeting on “Food Safety in relation to Ready-to-Eat Foods Sold by Vending Machines” for trade members on 20 March.

4.  The 84th Meeting of the Trade Consultation Forum
The 84th meeting of the Trade Consultation Forum was held on 14 March.  The CFS and the trade exchanged their views on various topics including “Risk Assessment Study on PAH in Food”, “Glycidyl Fatty Acid Esters & 3-monochloropropane-1,2-diol Ester in Food”, “Phthalates in Food”, “Food Safety Advice for Online Grocery Shopping and Delivery”, and “Control Measures on Food Imported from Japan”.  For details of the event, please visit:

5.  Briefing on Food Laws, Food Import Control and Nutrition Labels in Hong Kong for Students of Bachelor’s Degree Programmes, Hong Kong Metropolitan University (HKMU)
The CFS held a briefing on food laws, food import control and nutrition labels in Hong Kong for students of Bachelor’s degree programmes, HKMU on 20 March to give information on the role of the Food and Environmental Hygiene Department (FEHD) in the control of imported food and the relevant laws.  These foods include milk, milk beverages, frozen confections, game, meat, poultry and eggs.  The briefing covered topics such as control measures on food imported by air, land and sea, the duties of relevant offices (e.g. Airport Offices, Man Kam To Food Control Point and Waterfront Offices), as well as control measures taken by the CFS against food imported from Japan after the commencement of the discharge of treated nuclear wastewater into the ocean by the Japanese Government since 24 August 2023.  It enabled the students to have a full understanding of the control of imported food in Hong Kong.  Moreover, the CFS staff explained what pre-packaged food is and the legal requirements on labels and nutrition labels for pre-packaged food sold in Hong Kong.  There was also a question and answer session for interaction and exchanges with the students.

6.  Promotion of the Habit of Eating Adequate Fruit by CFS and the Department of Health (DH)

The CFS has always supported the “Joyful Fruit Month” initiated by the DH.  The campaign aims to promote the habit of eating adequate fruit every day and has received widespread support from schools and various sectors of the community over the years.

In April this year, the CFS even put up community posters with the theme of “Joyful Fruit Month” in public markets under the FEHD to continue to create a cheerful atmosphere and disseminate health messages.

7.  CFS's Talk on Preparing Noodles, Pasta and Rice Safely to Prevent Food Poisoning (including Bongkrekic Acid Poisoning)
Recently, a fatal food poisoning case caused by the consumption of food containing bongkrekic acid occurred in Taiwan.  In view of this, the CFS specially held a talk for the trade on 22 April mainly to explain the food safety risks posed by bongkrekic acid produced in food and the points to note when preparing and cooking such food.

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How to Enjoy Oysters with Peace of Mind?

The oyster season has come, do you fancy some raw oysters?  But before you put them into your mouth, wait a moment and take a look at the information below. 

Beware of the microbiological and chemical risks of oysters
Since oysters constantly draw in water, they tend to accumulate metallic contaminants from contaminated seawater and pathogens, including norovirus, Vibrio bacteria and hepatitis A virus.  Consumption of raw or undercooked oysters may result in food poisoning caused by infection of these pathogens.

Pre-shucked oysters pose higher risks
Oysters may be exposed to micro-organism, dirt, mud and detritus, and contaminated during the shucking process.  Once shucked, oysters will die.  These pre-shucked oysters (also known as packaged ready-to-eat raw oysters) will deteriorate quickly if they are not kept at a low temperature to limit bacterial growth during transportation and storage.

Maximum level of metal in food as prescribed by law

Excessive dietary exposure to metallic contaminants may pose various adverse health effects.  In Hong Kong, the Food Adulteration (Metallic Contamination) Regulations list the maximum levels of metal in specified foods (including common seafood). 

The CFS has been taking samples of oysters and related products at the import, wholesale and retail levels for chemical and microbiological testing under its routine Food Surveillance Programme.  From January 2020 to October 2023, over 2 500 samples of oysters and related products were collected for chemical and microbiological testing.  Except for two imported raw oyster samples which were found to contain excessive cadmium and E. coli respectively, all samples passed the tests.  The overall satisfaction rate was over 99.9%. 

Tips for enjoying oysters with ease of mind

Food Safety Quiz

1.  What is the concentration of phytohaemagglutinin in broad beans (Vicia faba), expressed as a percentage of that in red kidney beans?
  1. 1-4%
  2. 5-10%
  3. 11-14%
  4. 15-20%


2.  Campylobacters can tolerate higher growth temperature. What is their optimum growth temperature?
  1. 32°C
  2. 42°C
  3. 52°C
  4. 62°C
3.  To minimise the formation of process contaminants when using an air flyer, we should:


  1. Avoid cooking food at too high a temperature for too long
  2. Trim the fat present in the food before air-flying
  3. Parboil the food before air-flying
  4. All of the above


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Food Safety Tips for Using Air Fryers

The air fryerNote 1 is a popular home appliance as it is able to cook food quickly with little oil, with a resulting texture which resembles that produced by deep frying.  Despite its name, it is actually a small convection oven with hot air circulated by a fan.

To prevent food poisoning, cook food thoroughly, especially for larger chunks of food. Do not overload air fryers. Turn the food occasionally when cooking.  Like any high-temperature dry-heat cooking methodNote 2, air frying is prone to formation of process contaminants like acrylamide and polycyclic aromatic hydrocarbons (PAHs).  To minimise their formation, do not cook food at too high a temperature for too long.  Aim for a golden-brown colour when air frying starchy food.  Trimming the fat present and parboiling the food before air-frying can also help to reduce the formation of process contaminants. 

Consumers should maintain a balanced diet with plenty of vegetables and fruits and keep the total amount of fat and salt in check. 

Note 1: To find out about “Is Air Frying a 'Lesser Evil' Version of Deep Frying?”, please browse the following webpage:
Note 2: For more details on “Dry-heat Cooking and Process Contaminants”, please browse the following webpage: