🍎 Formol number of fruit and vegetable juices and related products — after adding formaldehyde solution, the H+ ion released from each amino acid molecule is titrated potentiometrically with NaOH solution; result in ml of 0.1 mol/l NaOH per 100 ml of sample as a measure of the amino acid content (histidine, proline and hydroxyproline react incompletely); PN-EN 1133:1999 (withdrawn standard)

Food chemistry PN-EN 1133

Overview

WHAT THE STANDARD COVERS. The "Scope" field of the PKN card, in full: "A method is described for determining the formol number in fruit and vegetable juices and in related products. The formol number is expressed as the number of millilitres of sodium hydroxide solution, c(NaOH)=0.1 mol/l, consumed per 100 ml of the test sample. After formaldehyde solution is added to the test sample, one H+ ion is released from each molecule of amino acid present in the sample. This ion is then titrated potentiometrically with sodium hydroxide solution. The formol number is therefore a measure of the amino acid content of the sample, with the following reservations: the secondary amino groups of histidine do not take part in the reaction, and the groups of proline and hydroxyproline react to about 75 percent. Tertiary nitrogen and guanidine groups do not take part in the reaction. Details of interlaboratory tests on precision and the repeatability and reproducibility values of the method are given" (our translation; no full stop at the end on the card). We did not have the text of the standard (8 pages).

STATUS (card as of 13.10.2026). The card of PN-EN 1133:1999 (Polish version) bears the heading "Withdrawn": publication 23-09-1999, "Withdrawal date: 09-04-2024", 8 pages, price group D, Food, Agriculture and Forestry Sector, KT 38 Fruit and Vegetable Products, "Adopts: EN 1133:1994 [IDT]", ICS 67.160.20; there are no "Replaces" or "Replaced by" fields. The PKN search under "formolowej" (formol, 13.10.2026) returns only this standard. At other publishers: according to the Standard Norge catalogue (13.10.2026) NS-EN 1133:1994 (committee CEN/TC 174) has the status "Withdrawn" dated 23 February 2024, with no replacing standard named. We found no current standard on the formol number of juices in the PKN catalogue.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database from the production server, refreshed on 12.10.2026). The notation "EN 1133" (without the ISO element — "PN-EN ISO 1133" is the standard on the melt flow rate of plastics) appears in 8 records at 7 laboratories, always as "PN-EN 1133:1999" (at AB 592 next to "IFU No. 30 (Rev. 2005)", at AB 1095 with the location mark "Ł"); in the current PCA documents (read on 12–13.10.2026; issues from 30.10.2025 — AB 452 — to 04.08.2026 — AB 370) — in 8 rows at the same laboratories; a search of all downloaded PCA documents found no laboratories outside the database copy, no row with the number is set in bold italics, and no pages are repeated in any document. The "Laboratories" tab (search term "PN-EN 1133") shows all 7 laboratories — checked with the tab query on the labcoda.pl production server on 13.10.2026.

WHAT THE LABORATORIES TEST (database copy and PCA documents). Test object: juices — AB 313, AB 592; fruit juices and nectars and vegetable juices — AB 285; fruit juices, fruit nectars, vegetable juices and separately fruit-and-vegetable juices — AB 370; juices, nectars, fruit, vegetable and fruit-and-vegetable purées, soft drinks — AB 452; fruit and vegetable juices — AB 704; fruit and vegetable products — AB 1095. Technique: potentiometric titration — 7 entries; "titrimetric method" — the first entry of AB 370. Ranges: (0.1–60.0) and (3.0–35.0) ml 0.1 mol NaOH/100 ml — AB 370; (1–51) ml — AB 592; (1.0–50.0) ml — AB 704; (1.0–30) ml 0.1 N NaOH/100 ml — AB 452; (2–30) ml — AB 313; (3.6–68.2) ml — AB 285; (1.5–50.0) mmol NaOH/100 ml — AB 1095.

ALONGSIDE THIS STANDARD. In the database copy the formol number is determined by 7 laboratories — all according to this standard; the only other document in these entries is the IFU method No. 30 (Rev. 2005) at AB 592. In the same PCA documents other standards of the series of juice test methods stand nearby, among them PN-EN 1132 (pH), PN-EN 1135 (ash), PN-EN 1136 (phosphorus), PN-EN 1138 (L-malic acid), PN-EN 1141 (proline) and PN-EN 12143 (soluble solids, refractometry); the determination of the pH of juices according to PN-EN 1132 and of soluble solids according to PN-EN 12143 is described in separate Knowledge Base entries.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. First — what the number measures: it is a measure of the amino acid content with the reservations from the card — the secondary amino groups of histidine do not react, proline and hydroxyproline react to about 75 %, tertiary nitrogen and guanidine groups do not react; the formol number is therefore not the total amino acid content. Second — unit: the card expresses the result in ml of 0.1 mol/l NaOH solution per 100 ml of sample; 1 ml of such a solution is 0.1 mmol NaOH, so the range of AB 1095 given in "mmol NaOH/100 ml" differs from the unit of the card by a factor of ten — when comparing results, check in which unit the laboratory reports the result. Third — titration: the card speaks of potentiometric titration, while one entry of AB 370 gives "titrimetric method" without this qualifier. Fourth — test object: the card speaks of fruit and vegetable juices and related products; whether this includes soft drinks (AB 452) and fruit and vegetable products (AB 1095) does not follow from the card. Fifth — status: the standard has been withdrawn since 09.04.2024 without a successor being named.

WHAT WE DO NOT GIVE. We did not have the text of the standard — we do not give the concentration and volume of the formaldehyde solution, the pH to which the titration is carried out, sample preparation (e.g. degassing, filtration, dilution), the calculation formula or the repeatability and reproducibility values. We did not read the content of the IFU method No. 30.

Method principle

Formaldehyde solution is added to the juice sample; one H+ ion is released from each molecule of amino acid present in the sample and titrated potentiometrically with sodium hydroxide solution. The formol number is the number of millilitres of 0.1 mol/l NaOH consumed per 100 ml of sample — a measure of the amino acid content, where histidine, proline and hydroxyproline react incompletely and tertiary nitrogen and guanidine groups do not react (PKN card). WE DO NOT GIVE details — we did not have the text of the standard.

Applications

• Fruit and vegetable juices and related products — formol number as a measure of the amino acid content (PKN card)
• Juices, nectars, purées, soft drinks, fruit and vegetable products — in the current accreditation scopes of 7 laboratories

Key parameters

Standard

Standard number

PN-EN 1133:1999

Title (PL)

Soki owocowe i warzywne — Oznaczanie liczby formolowej

Title (EN)

Fruit and vegetable juices — Determination of the formol number

Step-by-step procedure

1. Sample

   Measured volume of juice; WE DO NOT GIVE the preparation. PN-EN 1133:1999 withdrawn on 09-04-2024 (card as of 13.10.2026).

2. Addition of formaldehyde

   Formaldehyde releases one H+ ion from each amino acid molecule (PKN card).

3. Titration

   Potentiometrically with NaOH solution (PKN card); WE DO NOT GIVE the end point.

4. Result

   Number of ml of 0.1 mol/l NaOH consumed per 100 ml of sample (PKN card); the unit of the result in the report.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Formaldehyde and sodium hydroxide — safety rules of a chemical laboratory and the safety data sheets of the substances
• SUBJECT-MATTER NOTE: the formol number is not the total amino acid content — histidine, proline and hydroxyproline react incompletely (PKN card)

Frequently asked questions